To evaluate the effectiveness of a multifactorial fall prevention program in prespecified subgroups of nursing home residents. Secondary analysis of a cluster-randomized, controlled trial. Six nursing homes in Germany. Seven hundred twenty-five long-stay residents; median age 86; 80% female. Staff and resident education on fall prevention, advice on environmental adaptations, recommendation to wear hip protectors, and progressive balance and resistance training. Time to first fall and the number of falls. Falls were assessed during the 12-month intervention period. Univariate regression analyses were performed, including a confirmatory test of interaction. The intervention was more effective in people with cognitive impairment (hazard ratio (HR)=0.49, 95% confidence interval (CI)=0.35-0.69) than in those who were cognitively intact (HR=0.91, 95% CI=0.68-1.22), in people with a prior history of falls (HR=0.47, 95% CI=0.33-0.67) than in those with no prior fall history (HR=0.77, 95% CI=0.58-1.01), in people with urinary incontinence (HR=0.59, 95% CI=0.45-0.77) than in those with no urinary incontinence (HR=0.98, 95% CI=0.68-1.42), and in people with no mood problems (incidence rate ratio (IRR)=0.41, 95% CI=0.27-0.61) than in those with mood problems (IRR=0.74, 95% CI=0.51-1.09). The effectiveness of a multifactorial fall prevention program differed between subgroups of nursing home residents. Cognitive impairment, a history of falls, urinary incontinence, and depressed mood were important in determining response.