In a Belgian population group of 15 954 male and 2116 female soldiers and their spouses the relationship between coffee drinking and serum cholesterol has been studied. A moderate but highly significant monotonic positive relationship between coffee drinking and both serum total and non-high density lipoprotein (HDD-cholesterol was observed in men (p<0.001) even when adjusted for the confounding effects of age, body mass index, smoking, alcohol, and dietary fat and cholesterol intake. Men drinking at least three cups of coffee daily had a mean level of serum total cholesterol about 4 mg/dl and of non-HDL-cholesterol about 3 mg/dl higher than those who did not drink coffee. No significant effect of coffee drinking on HDL-cholesterol was observed in men. In women coffee-drinking did not influence any of the measured serum liplds.