Background: This study examines effects of mobility and multimorbidity on hospitalization and inpatient and postacute care (PAC) facility days among older men. Methods: Prospective study of 1,701 men (mean age 79.3 years) participating in Osteoporotic Fractures in Men (MrOS) Study Year 7 (Y7) examination (2007-2008) linked with their Medicare claims. At Y7, mobility ascertained by usual gait speed and categorized as poor, intermediate, or good. Multimorbidity quantified by applying Elixhauser algorithm to inpatient and outpatient claims and categorized as none, mild-moderate, or high. Hospitalizations and PAC facility stays ascertained during 12 months following Y7. Results: Reduced mobility and greater multimorbidity burden were independently associated with a higher risk of inpatient and PAC facility utilization, after accounting for each other and traditional indicators. Adjusted mean total facility days per year were 1.13 (95% confidence interval [CI] = 0.74-1.40) among men with good mobility increasing to 2.43 (95% CI = 1.17-3.84) among men with poor mobility, and 0.67 (95% CI = 0.38-0.91) among men without multimorbidity increasing to 2.70 (95% CI = 1.58-3.77) among men with high multimorbidity. Men with poor mobility and high multimorbidity had a ninefold increase in mean total facility days per year (5.50, 95% CI = 2.78-10.87) compared with men with good mobility without multimorbidity (0.59, 95% CI = 0.37-0.95). Conclusions: Among older men, mobility limitations and multimorbidity were independent predictors of higher inpatient and PAC utilization after considering each other and conventional predictors. Marked combined effects of reduced mobility and multimorbidity burden may be important to consider in clinical decision-making and planning health care delivery strategies for the growing aged population.