It remains controversial whether in human immunodeficiency virus (HIV)-positive pregnant women an increased rate of preterm delivery is associated with highly active antiretroviral therapy (HAART). Since 1995 the management and outcome of all HIV-infected pregnant women delivering at St. Mary's Hospital London have been prospectively documented. The prevalence of preterm delivery and the correlation between gestational age and type of antiretroviral therapy were sought: preterm delivery occurred in 14.2% of the 211 deliveries. Initiation of HAART during pregnancy was associated with an increased risk of preterm delivery. This was independent of maternal health and class of antiretroviral therapy.