The effects of weight change on serum lipid changes were assessed in a sample of 56 obese children randomly assigned to family-based behavioral obesity treatment vs controls given no treatment. Fasting serum lipid levels, height, weight, and fitness were measured at program entry and after 6 months of treatment. Children assigned to treatment showed significantly greater relative weight and weight changes than children in the control group, and the weight changes were significantly related to reductions in fasting serum triglyceride and total serum cholesterol levels and increases in high-density lipoprotein serum cholesterol. Results after 5 years of follow-up available for a small sample of treated children showed that a change in relative weight and fitness from 6 months to 5 years was also associated with changes in the high-density lipoprotein level. These results suggest that weight control in obese preadolescent children may be associated with improvement in lipoprotein profiles.