We report on a nonrandomized intervention cohort study to increase exclusive breast-feeding rates for 6 months after delivery in HIV-positive and HIV-negative women in KwaZulu-Natal, South Africa. Lay counselors visited women to support exclusive breast-feeding: four times antenatally, four times in the first 2 weeks postpartum and then fortnightly to 6 months. Daily feeding practices were collected at weekly intervals by separate field workers. Cumulative exclusive breast-feeding rates from birth were assessed by Kaplan-Meier analysis and association with maternal and infant variables was quantified in a Cox regression analysis. One thousand, two hundred and nineteen infants of HIV-negative and 1217 infants of HIV-positive women were followed postnatally. Median duration of exclusive breast-feeding was 177 (R = 1-180; interquartile range: 150-180) and 175 days (R = 1-180; interquartile range: 137-180) in HIV-negative and HIV-positive women, respectively. Using 24-h recall, exclusive breast-feeding rates at 3 and 5 months were 83.1 and 76.5%, respectively, in HIV-negative women and 72.5 and 66.7%, respectively, in HIV-positive women. Using the most stringent cumulative data, 45% of HIV-negative and 40% of HIV-positive women adhered to exclusive breast-feeding for 6 months. Counseling visits were strongly associated with adherence to cumulative exclusive breast-feeding at 4 months, those who had received the scheduled number of visits were more than twice as likely to still be exclusively breast-feeding than those who had not (HIV-negative women: adjusted odds ratio: 2.07, 95% confidence interval: 1.56-2.74, P < 0.0001; HIV-positive women: adjusted odds ratio: 2.86, 95% CI 2.13-3.83, P < 0.0001). It is feasible to promote and sustain exclusive breast-feeding for 6 months in both HIV-positive and HIV-negative women, with home support from well trained lay counselors.