This study aimed to examine risky sexual behavior, its associated factors and HIV infection among immigrants. A participatory cross-sectional survey was conducted with 1187 immigrants at the National Immigrant Support Centre, in Lisbon (52.2% female; 34.0% Africans, 33.8% Brazilians, 32.2% Eastern Europeans). About 38% of participants reported ≥ 2 sexual partners in the previous year, 16.2% both regular and occasional sexual partners (last 12 months), 33.1% inconsistent condom use with occasional partners, and 64% no condom use in the last sexual intercourse. Unprotected sex in the last sexual intercourse was more likely among women, Africans, those older, with elementary education, those married and those who didn't receive free condoms in the previous year. No condom use was less likely among those having only occasional sexual partners and both regular and occasional sexual partners. One third of participants had never been tested for HIV. Those never tested reported more frequently inconsistent condom use than those ever tested. Overall, 2.0% reported being HIV positive (2.5% of men; 4.4% of Africans); 4.3% admitted having a STI in previous year. HIV-positive immigrants reported high-risk sexual behaviors. Tailored interventions to promote awareness of HIV serostatus among immigrants as well as culturally adapted risk reduction strategies should be strengthened.