BACKGROUND: Poor growth is an indication for antiretroviral therapy (ART) and a criterion for treatment failure. We examined variability in growth response to ART in 12 programs in Malawi, Zambia, Zimbabwe, Mozambique, and South Africa. METHODS: Treatment naïve children aged <10 years were included. We calculated weight for age z scores (WAZs), height for age z scores (HAZs), and weight for height z scores (WHZs) up to 3 years after starting ART, by using the World Health Organization standards. Multilevel regression models were used. RESULTS: A total of 17 990 children (range, 238-8975) were followed for 36 181 person-years. At ART initiation, most children were underweight (50%) and stunted (66%). Lower baseline WAZ, HAZ, and WHZ were the most important determinants of faster catch-up growth on ART. WAZ and WHZ increased rapidly in the first year and stagnated or reversed thereafter, whereas HAZ increased continuously over time. Three years after starting ART, WAZ ranged from-2.80 (95% confidence interval [CI]:-3.66 to-2.02) to-1.98 (95% CI:-2.41 to 2 1.48) in children with a baseline z score <-3 and from-0.79 (95% CI:-1.62 to 0.02) to 0.05 (95% CI:-0.42 to 0.51) in children with a baseline WAZ ≥-1. For HAZ, the corresponding range was-2.33 (95% CI:-2.62 to-2.02) to-1.27 (95% CI:-1.58 to-1.00) for baseline HAZ <-3 and 20.24 (95% CI:-0.56 to 0.15) to 0.84 (95% CI: 0.53 to 1.16) for HAZ ≥ 21. CONCLUSIONS: Despite a sustained growth response and catch-up growth in children with advanced HIV disease treated with ART, normal weights and heights are not achieved over 3 years of ART. Copyright © 2012 by the American Academy of Pediatrics.