Background Sexually transmitted infections (STIs) are a major public health problem in Europe and in Portugal, their incidence has been increasing since the 90s. Although STIs are among the most frequently reported infections globally, they still go often underdiagnosed. Their under notification is also a problem in Portugal. The aim of this study is to describe STIs' notifications in the area of the groups of primary healthcare centers of Loures-Odivelas (ACES LO), between 2015-2019. Methods An observational, descriptive, quantitative study was performed. Data was collected in January 2020, from the National System of Epidemiological Surveillance Database. Variables included for each STIs notification were age and sex. Univariate descriptive analysis and evolution trends were performed for each variable. Results A total of 638 cases of STIs were reported from 2015 to 2019. The number of reported cases increased from 87 to 197 cases (126.4%). The annual mean incidence of HBV and HCV notifications were 8 and 4, respectively. There was an increase in reported cases of syphilis (33 to 57), HIV (13 to 29), chlamydia (13 to 46) and gonorrhea (18 to 51). In 2019, 30.9% of the notified cases were syphilis infections, 23.5% gonorrhea infections, 22.1% chlamydia infections and 13.2% HIV infections.Males comprised 460 cases (72.1%), and, in patients aged between 15 and 44 years old, 484 cases (75.9%) were reported. From 2015 to 2019, the co-infections of gonorrhea and chlamydia increased from 2 to 10 cases (25.0%). In 2019, 17.5% of the notified cases of gonorrhea were co-infections. Conclusions The modification of risk behaviors and the appropriate treatment of infected people, including infected partners, are determinant to prevent recurrent infections and to interrupt the transmission cycle. Increasing notification should facilitate the monitoring of STIs' trends, contributing to the implementation of appropriate interventions and for better decision-making in public health. Key messages Campaigns about sexual health promotion are important to increase safer sexual health practices. More notifications contribute to better data quality and more robust decision-making.