OBJECTIVE: To investigate trends in child malnutrition in six countries in southern Africa, in relation to the HIV epidemic and drought in crop years 2001/2 and 2002/3. DESIGN: Epidemiological analysis of sub-national and national surveys with related data. SETTING: Data from Lesotho, Malawi, Mozambique, Swaziland, Zambia and Zimbabwe, compiled and analysed under UNICEF auspices. SUBJECTS: Secondary data: children 0-5 years for weight-for-age; HIV prevalence data from various sources especially antenatal clinic surveillance. RESULTS: Child nutritional status as measured by prevalence of underweight deteriorated from 2001 onwards in all countries except Lesotho, with very substantial increases in some provinces/districts (e.g. from 5 to 20% in Maputo (Mozambique, 1997-2002), 17 to 32% in Copperbelt (Zambia, 1999-2001/2) and 11 to 26% in Midlands province (Zimbabwe, 1999-2002)). Greater deterioration in underweight occurred in better-off areas. Areas with higher HIV/AIDS prevalences had (so far) lower malnutrition rates (and infant mortality rates), presumably because more modern areas--with greater reliance on trade and wage employment--have more HIV/AIDS. Areas with higher HIV/AIDS showed more deterioration in child nutrition. A significant area-level interaction was found of HIV/AIDS with the drought period, associated with particularly rapid deterioration in nutritional status. CONCLUSIONS: First, the most vulnerable may be households in more modern areas, nearer towns, to whom resources need to be directed. Second, the causes of this vulnerability need to be investigated. Third, HIV/AIDS amplifies the effect of drought on nutrition, so rapid and effective response will be crucial if drought strikes again. Fourth, expanded nutritional surveillance is now needed to monitor and respond to deteriorating trends. Finally, with or without drought, new means are needed of bringing help, comfort and assistance to the child population.