Using event analysis, this study describes the most recent sexual events of drug-using women and their male partners and identifies relationship-specific and event-specific determinants of condom use. Women drug users (n = 320) were recruited from the streets of East Harlem. After validation of drug use, they participated in structured interviews and were offered HIV testing and counseling. Interview topics included the following: (1) demographic characteristics of respondents, (2) relationship factors, including age difference, race/ethnicity concordance, and HIV serostatus of partners, and (3) event-specific factors, including sexual repertoire, communication about condom use, and perception of HIV risk. Univariate and multivariate analyses identified five major variables associated with event-specific condom use: (1) closeness to partner, (2) perceived dyadic serostatus, (3) sexual repertoire, (4) communication about condoms, and (5) perceived control of condom use. Behavioral interventions to reduce sexual risk should target dyads with long-standing sexual relationships and focus on the dynamics of the relationship, especially the issues of dyadic serostatus, intimacy, communication, and control.