Background Treatment studies of depression in residential care are limited. Reports of predictors of response are rare. In the largest nursing home prospective antidepressant trial reported, we examined predictors of response. Methods This was a 12-week open-label study of mirtazapine orally disintegrating tablets performed in 30 US nursing homes. Subjects were men and women aged >= 70, with a Mini Mental State Exam (MMSE) score >= 10, who had a depressive disorder that required antidepressant treatment. Mirtazapine was started at 15 mg at bedtime, and adjusted to 15-45 mg/day. A 16-item Hamilton Depression Rating Scale was used to assess depression at baseline, weeks 2, 4, 8, and 12 or early termination. Results One hundred and twenty-four patients received at least one dose of study drug and of these, 119 had at least one post-drug assessment. Mean age was 82.9 years and 72% were female. Response rates at 12 weeks were 47% on the HAMD and 54% on the CGI. Age, sex, MMSE score, medical burden, history of prior depression, and baseline HAMD saverity were not significantly associated with HAMD response (>= 50% improvement) and in most cases correlations were trivial, <0.1. Advanced age, medical burden, and cognitive impairment did not predict adverse events. Conclusions In this sample of depressed nursing home residents treated with mirtazapine orally disintegrating tablets, advanced age, medical illness, and cognitive impairment did not predict response. The findings suggest that these variables need not be viewed as obstacles to treatment. Copyright (c) 2007 John Wiley & Sons, Ltd.