In Lesotho, the risk of mother-to-child-transmission (MTCT) of HIV is substantial; women of childbearing age have a high HIV prevalence rate (26·4%), low knowledge of HIV status and a total fertility rate of 3·5 births per woman. An effective means of preventing MTCT is to reduce unwanted fertility. This paper examines the unmet need for contraception to limit and space births among HIV-positive women in Lesotho aged 15–49 years, using the 2004 Lesotho Demographic and Health Survey. HIV-positive women have their need for contraception unmet in almost one-third of cases, and multivariate analysis reveals this unmet need is most likely amongst the poor and amongst those not approving of family planning. Urgent action is needed to lower the level of unmet need and reduce MTCT. A constructive strategy is to improve access to family planning for all women in Lesotho, irrespective of HIV status, and, more specifically, integrate family planning with MTCT prevention and voluntary counselling and testing services.