BACKGROUND: Older adults commonly use loop diuretics, which can increase urinary calcium excretion, leading to potential bone loss. Studies examining the association between loop diuretics and bone mineral density (BMD) are lacking, particularly those involving men. METHODS: In this cohort study, we ascertained medication use (interviewer-administered questionnaire verified with inspection of medication containers) and measured the BMD of the total hip and 2 subregions (by dual-energy x-ray absorptiometry) at baseline and at a second visit an average of 4.6 years later among 3269 men aged 65 years and older. RESULTS: Eighty-four men were categorized as continuous users of loop diuretics, 181 as intermittent users of loop diuretics, and 3004 men as nonusers of loop diuretics. After adjustment for age, baseline BMD, body mass index, weight change from baseline, physical activity, clinic site, perceived health status, cigarette smoking status, diabetes mellitus, chronic obstructive pulmonary disease, congestive heart failure, hypertension, and statin use, the average annual rate of decline in total hip BMD steadily increased from -0.33% (95% confidence interval [CI], -0.36% to -0.31%) for nonusers,to -0.58% (95% CI, -0.69% to -0.47%) for intermittent users, and to -0.78% (95% CI, -0.96% to -0.60%) for continuous users. Findings were similar for change in BMD at the femoral neck and trochanter. CONCLUSIONS: We conclude that loop diuretic use in older men is associated with increased rates of hip bone loss. These results suggest that the potential for bone loss should be considered when loop diuretics are prescribed to older patients in clinical practice.