In a 25-year follow-up study of 44,864 men with measured serum cholesterol levels, the testicular cancer hazard ratios for the serum cholesterol categories 5.7-6.9 and > or = 7.0 mmol l(-1) vs the reference category (<5.7 mmol l(-1)) were 1.3 and 4.5, respectively; P-value for trend=0.005. This highly significant association suggests that high-serum cholesterol is a risk factor for testicular cancer.