To determine the effect of an HIV-1 counselling programme on rates of HIV-1 infection and pregnancy in a large group of married couples in Kinshasa, DRC with discordant HIV-1 infection status, we conducted a baseline cross-sectional HIV-1 seroprevalence study in two large Kinshasa businesses. We identified 178 married couples (mean duration of marriage = 12.3 years) with discordant HIV-1 serostatus (92 M+F-/86 M-F+). Seroincidence and pregnancy rates were observed during 310 person-years of follow-up (PYFU). The 92 M+F- couples had an HIV-1 incidence of 3.7/100 PYFU and a pregnancy rate of 8.6/100. The 86 M-F+ couples had a pregnancy rate of 6.8/100 PYFU and an HIV-1 incidence of 6.8/100 PYFU. Couples seeking to have children but minimize their HIV-1 transmission risk frequently had unprotected sex only during the woman's perceived monthly fertility period. This strategy resulted in the birth of 24 live-born children and only one (4%; 95% CL = 0.0-21.6%) new HIV infection in couples having a child. Only 1 of 6 women who developed HIV-1 infection (16. 7%; 95 C.L. = 0-40.4%) became pregnant. While seronegative men had more extramarital sex once their wives' positive HIV-1 infection status became known, most of these episodes involved safe sex. Divorce was rare. This study provides additional information concerning issues of safe sex in married couples with discordant HIV-1 infection status, the dynamics of HIV transmission within couples and the effect of serostatus notification on the marriage and on intramarital and extramarital sexual behaviour in Kinshasa, Congo.