OBJECTIVE--To determine the impact of nutritional counseling on lipoprotein profiles in dyslipoproteinemic children. DESIGN--Retrospective case review. SETTING--An academic hospital-based pediatric lipid clinic in Boston, Mass. PARTICIPANTS--One hundred four newly referred children with primary dyslipoproteinemia. INTERVENTIONS--Nutritional recommendations were adapted from the National Cholesterol Education Program's step 2 diet. Three-day diet records were used to assess baseline and follow-up diets. RESULTS--Two thirds of the children continued to have excellent diets or improved their diets after counseling, but low-density lipoprotein cholesterol (LDL-c) values decreased by 15% or more in only 19% of children. The observed change in LDL-c was not significantly associated with nutritional counseling. However, a strong correlation was evident between dietary interventions and concentration of high-density lipoprotein cholesterol (HDL-c) values in serum. Marked fat restriction lowered HDL-c levels, while liberalization of use of fat, with emphasis on monounsaturates, in a subset of children following an excessively fat-restricted diet on presentation, appeared to improve HDL-c levels. CONCLUSIONS--After nutritional counseling, LDL-c levels decreased by 15% or more in only 19% of dyslipoproteinemic children referred for treatment. There were no clear predictors of LDL-c responsiveness, but changes in dietary fat intake appeared to significantly influence HDL-c levels.