BACKGROUND: Nevirapine has been widely used in pregnancy for its efficacy, low pill burden, bioavailability and rapid transplacental transfer. Concern about nevirapine toxicity during pregnancy has emerged over recent years. OBJECTIVES: The aims of the study were to document the frequency of cutaneous and hepatic toxicity secondary to nevirapine use during pregnancy and to compare rates in women starting nevirapine during the current pregnancy with those in women who had commenced nevirapine prior to the current pregnancy. DESIGN: This was a retrospective, comparative, five-centre study carried out in London, UK, in 1997-2003. METHODS: All HIV-1-infected women who received nevirapine as part of combination antiretroviral therapy (ART) during pregnancy were included in the study. Data on demographics, HIV infection risk, Centers for Disease Control and Prevention (CDC) status, surrogate markers at initiation of therapy, other medications hepatitis B and C virus coinfection and clinical data relating to potential toxicity were collated and analysed. RESULTS: Fifteen of 235 eligible women (6.4%) developed rash and eight (3.4%) developed hepatotoxicity, including four with coexistent rash, giving a combined incidence of 19 potential cases of nevirapine toxicity during pregnancy (8.1%). Alternative causes of rash/hepatotoxicity were suspected in seven cases and only 10 mothers (5.8%) discontinued nevirapine. Of the 170 women who commenced nevirapine during this pregnancy, 13 (7.6%) developed rash and eight (4.7%) hepatotoxicity, a combined incidence of 10%. Only two of 65 women with nevirapine exposure prior to this pregnancy developed rash (3.1%). CONCLUSIONS: Nevirapine-containing ART was well tolerated in this cohort of pregnant women. Although pregnancy did not appear to increase the risk of nevirapine-associated toxicity compared to published adult data, CD(4) count may be less predictive of toxicity in pregnancy.