Background: Homeless persons have been described as one of the most vulnerable populations worldwide, with higher morbidity and mortality of diseases associated with HIV occurrence. Seroprevalence of Toxoplasma gondii and HIV has been extensively studied in other vulnerable populations, however, no study to date have focused on their concomitant seroprevalence in homeless persons. Accordingly, the present study aimed to assess the concomitant seroprevalence of anti-T. gondii and anti-HIV antibodies and associated risk factors in homeless persons in a daytime homeless shelter of São Paulo, southeastern Brazil. Methods: Anti-T. gondii antibodies were detected by indirect fluorescent antibody test and anti-HIV levels by chemiluminescence enzyme immunoassay, with positive samples confirmed by rapid immunoblot assay. Results: Overall, IgG anti-T. gondii seropositivity was found in 43/120 (35.8%) homeless persons, with endpoint titers varying from 16 to 1,024. The only two pregnant women tested were negative for IgM by chemiluminescence enzyme immunoassay, with normal parturition and clinically healthy newborns in both cases. There were no statistical differences in the risk factors for anti-T. gondii serology (p>0.05). Anti- HIV seropositivity was found in 2/120 (1.7%) homeless persons, confirmed as HIV-1. One HIV seropositive individual was also sero-reactive to IgG anti-T. gondii, and both were negative to IgM anti-T. gondii. One HIV positive person was also diagnosed with syphilis, tuberculosis and body lice presence, while the other never returned for assistance. No evaluation of anti- HIV risk factors has been made due to the low seropositive rate. Conclusions: The anti-T. gondii prevalence herein was lower than other Brazilian populations, likely related to predominant intake of processed food such as ready-to-eat and fast-food meals, and thus, low ingestion of fresh salad and raw meat. On the other hand, the anti- HIV seropositivity was higher than the average of the general Brazilian population, with 0.4%. Despite the low prevalence of anti-T. gondii in homeless persons, clinical manifestations may be aggravated in HIV positive individuals. To the author's knowledge, this is the first study of anti-T. gondii serosurvey in homeless persons concomitantly assessed with anti-HIV seropositivity.