To identify risk factors involved in heterosexual transmission of human immunodeficiency virus (HIV), a cross-sectional study of HIV-seropositive men and their spouses was conducted in Nairobi, Kenya. Of 70 spouses, 40 (57%) were seropositive and 30 (43%) were seronegative for HIV. In univariate analysis, the presence of cervical ectopy (odds ratio, 4.7; P = .006) was the only statistically significant variable associated with HIV infection in women. After controlling for possible confounding variables using multivariate logistic regression analysis, the presence of cervical ectopy (odds ratio, 5.0; P = .007) remained the only independent predictor of HIV seropositivity. These findings suggest that cervical ectopy may be a newly identified risk factor for heterosexual transmission of HIV.