To study the association between serum calcium and serum lipids, data from 5394 men and 4800 women in the Belgian Interuniversity Research on Nutrition and Health (25-74 years) were used. By visual inspection of the data a linear increase of both total and HDL cholesterol with serum calcium levels was observed, consistently over all age groups and both sexes. In order to adjust the measured serum calcium concentrations for total serum protein, statistical analyses were performed using Parfitt's correction formula. Multivariate analysis showed in both sexes a highly significant positive association between corrected calcium and total cholesterol independent of age, systolic blood pressure, body mass index, serum uric acid, P/S ratio of diet, cholesterol intake, smoking, educational level and geographical area. The adjusted differences in total cholesterol between the lowest and highest quartile range of the calcium distribution were about 13 mg/dl for both men and women. Protein-corrected calcium was among the strongest correlates with total cholesterol. The analysis of the relation with HDL cholesterol revealed an effect modification by gender. For men no statistically significant correlation between calcium and HDL cholesterol was observed while for women a strong increase of HDL with protein-corrected calcium was found resulting in an adjusted difference of 2.5 mg/dl between the lowest and highest calcium quartile range.