Food insecurity is common among HIV-infected populations in resource-rich and resource-poor countries. We hypothesized that food insecurity would be associated with risky sexual behaviors. We examined this hypothesis among all sexually active participants (n = 154) in the Research on Access to Care in the Homeless (REACH) cohort in San Francisco. The outcomes were unprotected vaginal or anal sex and multiple sexual partners during the prior 90 days. Associations were examined using repeated measures multivariable logistic regression analyses. Food insecurity was independently associated with unprotected sexual activity (AOR = 2.01 for each five point increase in HFIAS scale, 95 % CI 1.31-3.10) and multiple sexual partners (AOR = 1.54 for each five-point increase in HFIAS scale, 95 % CI 1.05-2.29). Food insecurity is a risk factor for unprotected sexual activity and multiple sexual partners among homeless and marginally housed HIV-infected individuals in San Francisco. Measures to alleviate food insecurity may play a role in decreasing secondary HIV transmission.