Sexually transmitted infections (STIs) are a major problem worldwide. In addition, the spectrum of STIs is now expanding, including parasitic, bacterial, and viral infections. The study retrospectively describes the presence of enteric pathogens among 73 patients with gastrointestinal symptoms of enteritis and proctocolitis attending to an STI unit in Barcelona, Spain, between 2015 and 2016. Only patients investigated for intestinal parasitic infections were included in the study. Different diagnostic procedures were established for the detection of parasites, bacterial enteropathogens, and other STI agents. Entamoeba histolytica was the most prevalent pathogen in our cohort (20.5%), especially among individuals with proctocolitis. Contrarily, Giardia intestinalis was detected in 11.0% of patients, only associated with enteritis cases. Polymicrobial infections were common in our study (45.2%). Of note, 55.6% of shigellosis cases were coinfected with E. histolytica. The investigation highlights the importance of including parasites as differential gastrointestinal diagnosis, disregarding travel history, particularly among risk populations.