We investigated the severity and duration of hyperlipidemia in 59 nephrotic children during relapse and remission. Serum total cholesterol and triglyceride values were greater than or equal to 95th percentile for age and sex in all patients with minimal change nephrotic syndrome in relapse and in patients with non-MCNS and persistent proteinuria. Most of these patients also had a significant elevation of low- and very-low-density lipoproteins. A significant number of children with MCNS during prolonged remission had elevated serum concentrations of total cholesterol (46%), triglycerides (42%), LDL (29%), and VLDL (40%). Persistence and severity of lipid changes correlated well with duration of disease and frequency of relapses. Significantly decreased HDL and HDL/LDL were found in patients with non-MCNS and persistent proteinuria. Our results suggest that nephrotic children may have prolonged periods of hyperlipidemia even after clinical remission. In addition, some of these children with significantly decreased HDL/LDL may be at increased risk of developing premature atherosclerosis.