Sexual violence is a well-recognized global health problem, albeit with limited population-based data available from sub-Saharan Africa. We sought to measure the prevalence of forced sex in Kisumu, Kenya, and identify its associated factors. The data were drawn from a population-based cross-sectional survey. A two-stage sampling design was used: 40 clusters within Kisumu municipality were enumerated and households within each cluster selected by systematic random sampling. Demographic and sexual histories, including questions on forced sex, were collected privately using a structured questionnaire. The prevalence of forced sex was 13% (women) and 4.5% (men). After adjusting for age and cluster, forced sex among women was associated with transactional sex (OR 2.33; 95%CI 1.38-3.95), having more than two lifetime partners (OR 1.9; 95%CI 1.20-3.30), having postprimary education (OR 1.49; 95%CI 1.04-2.14) and a high economic status (OR 1.87; 95%CI 1.2-2.9). No factors were significantly associated with forced sex among the male respondents. Intimate partners were the most common perpetrators of forced sex among both women (50%) and men (62.1%). Forced sex prevention programs need to target the identified associated factors, and educate the public on the high rate of forced sex perpetrated by intimate partners.