To evaluate the impact of growth hormone deficiency (GHD) on lipid metabolism, serum lipid and apolipoprotein concentrations were measured in 64 GHD adult males (mean age, 27.1 +/- 4.7 years). Results were compared with those obtained from an age- and sex-matched control group. Total cholesterol, low-density lipoprotein (LDL) cholesterol, and apolipoprotein (apo) B levels were significantly higher in GHD patients (P < .001). In 14 patients (23%), total cholesterol concentration exceeded the 95th percentile for healthy adults. Total and LDL cholesterol were inversely related to plasma insulin-like growth factor-I (IGF-I). Apo B also tended to be negatively correlated with IGF-I; however, statistical significance was not reached (P = .054). High-density lipoprotein (HDL) cholesterol and plasma triglyceride concentrations were within normal limits, whereas apo A-1 and A-2 levels were only slightly different from normal. We conclude that GHD in adulthood is associated with mild hypercholesterolemia due to an increased LDL cholesterol level. An inverse relationship was established between LDL cholesterol concentration and GH secretory status.