Growth in terms of both height and weight was studied in a longitudinal sample consisting of ten children who all experienced the onset of acute leukemia between 18 months and 7 years of age. In spite of the lack of deviation in body size at birth, these children had somewhat higher values for attained size than the reference group one year before diagnosis. The information from this study showing a decrease in growth rate before the start of treatment, could suggest that the disease causes the growth failure. Growth rate for height increased with time from the first year of treatment, which could be correlated to a positive effect of medical treatment of the disease. These results indicate a very stable regulation of growth between 18 months and 12 years of age. The children dropped temporarily in mean one standard deviation (SD) corresponding to about 4 cm, from one year before the start of treatment to the end of the three years of treatment. It seems, however, that it is possible for the body to repair such a temporary growth inhibition as is seen in the catch-up growth during the following two years. Height measured in SD for the group two years after discontinuing treatment was practically the same as height at the time of the start of treatment. Children with leukemia during the first years of life and during the pubertal period may not show a similar growth pattern.