Objectives: Between 2013 and 2014, a third of Australian adults reported using the internet to investigate medical symptoms before consulting a medical practitioner. However, there is limited evidence regarding internet health information seeking behaviour (HISB) in sexual health. This study aims to determine the frequency, predictors and accuracy of internet HISB for sexual health self-diagnosis.Methods: A cross-sectional paper-based survey, available in English, Chinese and Thai, was conducted during April to August 2019 at the Sydney Sexual Health Centre (SSHC). Symptomatic patients were recruited to answer an 18-item survey on their HISB, self-assessed diagnosis, anxiety and health literacy. Survey responses were correlated with SSHC electronic medical record data including participant demographics and clinician diagnosis. Data analyses were performed using Stata V.14.Results: The majority of participants searched the internet (355; 79.1%) before attending clinic, and of these only 16.9% made a correct self-diagnosis. Multivariate analyses demonstrated that relative to Australian-born participants, people born in Asia were twice as likely to undertake internet HISB (adjusted OR (AOR) 2.41, 95% CI 1.25 to 4.64, p<0.01), and those born in Latin America were more likely to self-diagnose correctly (AOR 3.35, 95% CI 1.20 to 9.37, p<0.01). On average, participants who searched the internet scored higher relative to those who did not search, on measures of feeling generally tense (2.26, 95% CI 2.16 to 2.7 and 1.86, 95% CI 1.67 to 2.05, p<0.001), upset (1.96, 95% CI 1.85 to 2.08 and 1.53, 95% CI 1.35 to 1.72, p<0.001) and worried (2.55, 95% CI 2.44 to 2.65, and 2.16, 95% CI 1.95 to 2.38, p=0.001).Conclusions: This study has filled important gaps in the literature and highlighted the high prevalence of adults engaging in HISB for sexual health information. Of concern are the increased levels of anxiety and low accuracy of self-diagnoses associated with HISB. Strategies to direct patients to reputable and user-friendly health websites that mitigate anxiety and misinterpretation of online health information should be explored. [ABSTRACT FROM AUTHOR]