Combination antiretroviral therapy (ART) suppresses viral replication in HIV-infected children. The growth of virologically suppressed children on ART has not been well documented. We aimed to develop dynamic reference curves for weight-for-age z scores (WAZ) and height-for-age z scores (HAZ).

Children aged <11 years at ART initiation with continuously undetectable viral loads (<400 copies/ml) treated at seven South African ART programs with routine viral load monitoring were included. We used multilevel models to define trajectories of WAZ and HAZ up to 3 years and developed a web application to monitor trajectories in individual children.

A total of 4,876 children were followed for 7,407 person-years. Analyses were stratified by baseline z-scores and age, which were the most important predictors of growth response. The youngest children showed the most pronounced increase in weight and height initially but catch-up growth stagnated after 1–2 years. Three years after starting ART, WAZ ranged from −2.2 (95% Prediction interval −5.6 to 0.8) in children with baseline age >5 years and z-score <−3 to 0.0 (−2.7 to 2.4) in children with baseline age <2 years and WAZ >−1. For HAZ the corresponding range was −2.3 (−4.9 to 0.3) in children with baseline age>5 years and z-score <−3 to 0.3 (−3.1 to 3.4) in children with baseline age 2–5 years and HAZ >−1.

We have developed an online tool to calculate reference trajectories in fully suppressed children. The web application could help to define ‘optimal’ growth response and identify children with treatment failure.