Alterations in serum lipid values have been widely reported among persons infected with human immunodeficiency virus (HIV) type 1 treated with highly active antiretroviral therapy (HAART), but no data have yet been reported on changes from preseroconversion lipid values. To describe changes in serum cholesterol levels associated with HIV infection and antiretroviral medication exposure, and 1-time assessment of triglyceride levels post-HAART initiation. The Multicenter AIDS Cohort Study, a prospective study in which homosexual and bisexual men were enrolled and from which 50 of 517 HIV seroconverters were drawn for the analysis herein, who later initiated HAART, involving measurements of stored serum samples obtained between 1984 and 2002. Changes in levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) at 6 time points during an average of 12 years; 1-time assessment of triglyceride levels from the third post-HAART clinic visit. Among the 50 men, notable declines in mean serum TC (-30 mg/dL [-0.78 mmol/L]), HDL-C (-12 mg/dL [-0.31 mmol/L]), and LDL-C values (-22 mg/dL [-0.57 mmol/L]) were observed after HIV infection. Following HAART initiation, there were large increases in mean TC and LDL-C values (50 and 21 mg/dL [1.30 and 0.54 mmol/L], respectively); however, the mean changes from the preseroconversion values were 20 mg/dL (0.52 mmol/L) (95% confidence interval [CI], -1 to 41) and -1 mg/dL (-0.03 mmol/L) (95% CI, -25 to 22), respectively. Mean HDL-C remained below baseline levels throughout follow-up. The median value (interquartile range) of triglycerides was 225 mg/dL (2.54 mmol/L) (147-331 mg/dL). Before treatment, HIV infection results in substantial decreases in serum TC, HDL-C, and LDL-C levels. Subsequent HAART initiation is associated with increases in TC and LDL-C but little change in HDL-C. Increases in TC and LDL-C observed after about 3 years of HAART possibly represent a return to preinfection serum lipid levels after accounting for expected age-related changes.