Background: The growing trend of STIs in recent years was altered after the outbreak of the SARS-CoV-2 pandemic., Objectives: Describe the impact of the SARS-CoV-2 pandemic on STI declarations received during the pre-pandemic to pandemic period and estimate the number of STI cases expected for the pandemic period., Material and Methods: Descriptive analysis of STI declarations received during the pre-pandemic (2018-2019) and pandemic (2020-2021) periods. The influence of the number of positive cases of SARS-CoV-2 with the number of positive cases of STIs during the months of the pandemic was studied using a correlation model. Using the Holt-Wilson time series model, an estimate was made of the number of STI cases expected for the pandemic period., Results: The global incidence rate for all STIs in 2020 decreased by 18.3% compared to 2019. Chlamydia and syphilis presented a greater reduction in their incidence from 2019 to 2020 of 22.7% and 20.9%, respectively and 9.5% and 2.5% for gonorrhea and LGV. Estimates showed that in 2020 there would have been 44.6% more STIs than those declared. The proportions according to sex, country of birth and sexual orientation changed significantly in chlamydia and gonorrhea., Conclusions: The measures adopted for the prevention of SARS-CoV-2 infections were able to achieve an initial decrease in STI cases in 2020, however, this change was not maintained during 2021, which ended with higher incidences recorded to date., (Copyright © 2023 Elsevier España, S.L.U. All rights reserved.)