• Height velocities prior to and during weight reduction were determined retrospectively in 19 obese children selected because of a 10% or greater fall in weight for height. Mean duration of the weight reduction period was 9.7 months. All children were treated with a balanced calorie-deficit diet containing 1.5 to 2.0 g of protein per kilogram of ideal body weight per day. Height velocities were normalized by calculating the Z score for each one. Prior to weight reduction, the mean (±SD) Z score for height velocity was 2.32±2.47 units. Eleven patients were 2 SDs or more above the mean height velocity for age and sex. During weight reduction, the mean Z score for height velocity decreased significantly to 0.62±2.37 units. The change in Z score before and during weight reduction was significantly correlated with the change in weight but not with the change in weight for height. These data indicate that even mildly restrictive diets may be associated with a reduction in linear growth velocity. The implications of these observations for the risk of other adverse consequences of weight reduction are not clear. Nonetheless, our observations emphasize the importance of careful monitoring of obese children during mildly restrictive dietary therapy.