We aimed to identify factors associated with transmission of human immunodeficiency virus (HIV) from injecting drug users (IDUs) to their wives in Manipur, northeast India, where the prevalence of HIV among IDUs is 80% via a case-control study. One hundred and sixty-one HIV-infected IDUs and their wives were recruited from September 1996 to August 1997 inclusive. HIV status was determined by enzyme-linked immunosorbent assay (ELISA) plus Western blot, Interviews were administered anonymously. Regression analysis identified factors associated with transmission of HIV from IDU husbands to their non-injecting wives. Seventy-two wives (45%) were HIV-positive. Only 15% of the couples reported regular usage of condoms during intercourse. On multivariate analysis, a sexually transmitted disease (STD) in either member, reported by the husband, estimated duration of HIV in the husband for >8 years, and a history of blood transfusions were associated with infection in the wife. In conclusion, STDs are associated with transmission of HIV from husband to wife. Improved control of STDs, condom promotion, and improved blood screening are urgently needed in Manipur.