Problem: Sexually transmitted diseases (STDs) are a major cause of morbidity in the United States, with an estimated $15.9 billion in lifetime direct medical costs. Although the majority of STDs are diagnosed in the private sector, publicly funded STD clinics have an important role in providing comprehensive sexual health care services, including STD and HIV screening, for a broad range of patients. In certain cases, STD clinics often are the only source of sexual health care for patients, particularly among gay, bisexual, and other men who have sex with men (MSM)., Period Covered: 2010-2018., Description of the System: The STD Surveillance Network (SSuN) is an ongoing sentinel surveillance system for monitoring clinical information among patients attending STD clinics. SSuN is a collaboration of competitively selected state and city health departments that conduct facility-based sentinel surveillance in STD clinics. Information routinely collected through the course of patient encounters is obtained for all patients seeking care in the participating STD clinics. This information includes demographic, behavioral, and clinical characteristics (e.g., STD and HIV tests performed and STD and HIV diagnoses). This report presents 2010-2018 SSuN data from 14 STD clinics in five cities (Baltimore, Maryland; New York City, New York; Philadelphia, Pennsylvania; San Francisco, California; and Seattle, Washington) to describe the patient populations seeking care in these STD clinics. Estimated numbers and percentages of patients receiving selected STD-related health services were calculated for each year by using an inverse variance weighted random-effects model, adjusting for heterogeneity among SSuN jurisdictions. Trends in receipt of selected STD-related health services were examined and included HIV screening after an acute STD diagnosis among persons not previously known to have HIV infection, annual chlamydia screening among adolescent and young females, and extragenital chlamydia and gonorrhea screening among MSM., Results: During 2010-2018, the total number of annual visits made in the 14 participating STD clinics decreased 29.8% (from 145,728 to 102,275 visits), and the total number of unique patients examined in the clinics decreased 35.1% (from 94,281 to 61,172 patients). Decreases in the number of unique patients occurred both among men who have sex with women only (42.4%; from 37,842 in 2010 to 21,781 in 2018) and among females (51.4%; from 36,485 in 2010 to 17,721 in 2018). The decreases in the number of female patients were observed across all age groups, although they were more pronounced among females aged ≤24 years (66.4%; from 17,721 in 2010 to 5,962 in 2018). In contrast, the number of patients identified as MSM increased 44.0% (from 12,859 in 2010 to 18,512 in 2018), with the greatest increase among MSM aged ≥25 years (58.6%; from 9,918 in 2010 to 15,733 in 2018). Among visits during which an acute STD (defined as chlamydia, gonorrhea, or primary or secondary syphilis) was diagnosed, the percentage of visits during which an HIV test was performed within approximately 14 days of the STD diagnosis increased from 58.2% in 2010 to 70.2% in 2018. Among those patients tested, 1,672 HIV infections were identified, of which 84.0% were among MSM. Among females aged 15-24 years, the percentage screened for chlamydia in any calendar year increased from 88.6% in 2010 to 90.6% in 2018. However, because fewer females aged 15-24 years attended these clinics during the study period, the crude number of adolescent and young females tested for chlamydia decreased from 14,249 in 2010 to 4,507 in 2018. During 2010-2018, the percentage of females retested after their first positive chlamydia diagnosis during the same year ranged from 11.4% to 13.3%. During 2010-2018, the percentage of MSM tested for rectal chlamydia and rectal gonorrhea increased (from 54.7% to 57.8% and from 55.0% to 58.4%, respectively). During the same period, increases were noted in the percentage of MSM with diagnosed rectal chlamydia (from 15.5% in 2010 to 17.7% in 2018) and rectal gonorrhea (from 13.3% in 2010 to 17.1% in 2018). In contrast with pharyngeal chlamydia, pharyngeal gonorrhea screening was more common (from 69.5% in 2010 to 74.6% in 2018), and the percentage positive doubled during the study period (from 7.3% in 2010 to 14.8% in 2018). Pharyngeal chlamydia testing also increased (from 50.3% in 2010 to 72.9% in 2018), with concurrent decreases in positivity (from 4.2% in 2010 to 2.6% in 2018)., Interpretation: During 2010-2018, changes occurred in the demographic composition of patients attending STD clinics participating in SSuN. Understanding trends in the demographic profile of STD patients and services provided can help identify addressable gaps in STD control efforts and direct public health action. Overall, fewer females, especially those aged 15-24 years, accessed care in these STD clinics during the study period. Untreated STDs among adolescent and young females can have serious consequences, including pelvic inflammatory disease and infertility. Additional efforts to monitor where adolescent and young females seek care and to ensure they are receiving quality STD-related health services are needed, especially considering increases in reported cases of STDs among females. Increases in the number of MSM attending STD clinics present a unique opportunity to reach this population with STD and HIV prevention services. Although a large percentage of STD cases are diagnosed outside of STD clinics, publicly funded STD clinics are an important safety-net provider of STD-related health services and provide vital STD-related health services for patient populations at risk for the consequences of STDs and HIV infection., Public Health Actions: STD-related health services represent effective strategies for preventing STD and HIV transmission and acquisition or STD-related sequelae. Ensuring that all persons receive quality HIV and STD prevention and treatment services is vital for an effective public health approach to reducing STDs. STD clinics provide crucial safety-net services for preventing STD-related morbidity, including timely identification and treatment of curable STDs such as chlamydia, gonorrhea, and syphilis. Increases in the numbers of MSM attending STD clinics participating in SSuN provide additional opportunities for linking patients to high-impact HIV preventive services (e.g., pre-exposure prophylaxis), and the clinics are positioned to facilitate initiation or resumption of treatment among persons living with HIV., Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. No potential conflicts of interest were disclosed.