Symptomatic HIV infection was first diagnosed in an Irish child in 1985. A prospective study was initiated to determine the vertical transmission rate (VTR) of HIV and the average age of infant seroreversion and to monitor clinical, immunologic and virologic evidence for HIV infection in seroreverters. Ninety three HIV positive infants have been prospectively identified since 1985. The predominant underlying maternal risk factor for HIV infection is intravenous drug use (IVDU) (96 per cent). Of 93 infants, median gestational age was 40 weeks and median birth weight 3125 grams. Ninety-four per cent of infants were bottle fed. Currently 72 (77 per cent) infants are uninfected, 12 (13 per cent) are infected, 4 (4.5 per cent) are indeterminate and 5 (5.5 per cent) have been lost to follow up. The intermediate estimate of vertical transmission rate (VTR) is 14.3 per cent. The median age at documented seroreversion was 12 months. There are no significant differences between infected and non-infected children in male/female ratio, gestational age, mode of delivery or birth weight. Strategies to reduce the transmission of HIV among drug users in combination with routine antenatal screening and antiretroviral prophylaxis of vertical transmission are all measures which can reduce HIV infection in our children.