Factors predisposing to diuretic-induced acute gout were investigated in a case-control study. Seventy hypertensive patients with acute gout occurring during diuretic treatment were identified and matched for age and sex to 140 hypertensive controls who took diuretics but did not develop gout. Gout was related more strongly to the use of loop diuretics than thiazides, with 30% of cases taking a loop diuretic compared to 14% of controls (P less than 0.01). In a sub-group of men who took a thiazide and no other diuretic, gout was significantly associated with obesity (odds ratio 3.7, 95% confidence interval 1.4, 9.1) and high alcohol intake (odds ratio 3.3, 95% confidence interval 1.1, 9.8). In these patients, 23% of gout was attributable to obesity and 16% to high alcohol consumption. Approximately 40% of acute gout might have been prevented by avoiding thiazides in those 20% of men who weighed more than 90 kg and/or consumed more than 56 units of alcohol per week.