In Turkish adults, HDL cholesterol (HDL-C) levels are 10 - 15 mg/dl lower than those of adults in western Europe and the United States. In this study, we determined whether HDL-C levels in Turks are low from birth to adulthood and assessed the effect of socioeconomic status (SES) on plasma lipids and lipoproteins. Analyses of cord blood from 105 Turkish newborns showed low levels of plasma cholesterol (similar to 60 mg/dl) and HDL-C (similar to 30 mg/dl), consistent with results from other Western ethnic groups. Prepubescent 8- to 10-year-old Turkish boys and girls of upper (n = 82) and lower (n = 143) SES had high HDLC levels (50-60 mg/dl) similar to those of western European children. However, the cholesterol (154-158 mg/dl) and HDLC (55-58 mg/dl) levels of upper SES children were similar to 25 and similar to 12 mg/dl higher, respectively, than those of lower SES children. Height, weight, skinfold thickness, and estimated body fat were greater in the upper SES children and appeared to reflect dietary differences. Upper SES children consumed more total fat (similar to 35% vs. 25% of total calories), including more saturated fat of animal origin, and less carbohydrate (similar to 50% vs. 62% of total calories), consistent with their elevated plasma cholesterol levels. Carbohydrate intake correlated inversely with the HDL-C level. The HDL-C levels in the prepubescent children, especially those of higher SES, who consumed diets more like western Europeans, decreased markedly to adult levels, with males exhibiting a similar to 20 mg/dl decrease (from 58 to 37 mg/dl) and females a similar to 13 mg/dl decrease (from 55 to 42 mg/dl). SES did not affect HDL-C levels in adults. The profound decrease may reflect alterations in androgen/estrogen balance in Turks at puberty and a modulation of hepatic lipase affecting HDLC levels.