Longitudinal comparison of WHO standardized height z scores between children treated with HU and placebo. Z scores for height, weight, BMI, and HC were calculated by using SAS macros downloaded from the WHO Web site and controlled for gender and age. Data were averaged within each 3-month interval after treatment assignments with the baseline measurement used as the time 0. Student’s t test was used for comparison with the WHO normal population. Proc MIXED was used to analyze longitudinal data. BABY HUG children were larger than the WHO population on all parameters at the beginning of the study, and there was no difference between the treatment groups except for the BMI that was larger at each observation point in the HU group (trend not significant). There were no significant differences between the treatment groups for height, weight, and BMI at exit. The HC in the treatment group was slightly smaller but still within normal limit at the end of the study. Baseline z scores were the best predictors of z scores for all growth parameters.