Thiazide diuretics are known to raise total and LDL cholesterol. To assess whether chlorthalidone affected levels of putatively atherogenic small, dense LDL (LDL 3), we conducted a 12 week double blind randomized, placebo controlled clinical trial in 34 nonsmoking men aged 35 to 57 years with mild hypertension (DBP 90 to 104 mm Hg). Our a priori hypothesis that chlorthalidone raised LDL 3 levels was not confirmed. However, the fall in LDL 3 (P = .03) and total cholesterol (P = .08) associated with weight loss was attenuated by chlorthalidone. Since weight loss is commonly prescribed during the clinical management of hypertensives with concomitant hypercholesterolemia, consideration should be given to the attenuating effect of chlorthalidone on cholesterol reduction in the management of these patients.