We investigated whether frailty, defined as the accumulation of multiple, interacting illnesses, impairments and disabilities, is associated with psychiatric illness in older adults. Five-thousand-six-hundred-and-seventy-six community dwellers without dementia were identified within the Canadian Study of Health and Aging, and self-reported psychiatric illness was compared by levels of frailty (defined by an index of deficits that excluded mental illnesses). People with psychiatric illness (12.6% of those surveyed, who chiefly reported depression) had a higher mean frailty index value than those who did not. Older age was not associated with higher odds of psychiatric illness. Taking sex, frailty, and education into account, the odds of psychiatric illness decreased with each increasing year of age (OR 0.95; 95% CI, 0.94-0.97). Frailty was associated with psychiatric illness; for each additional deficit-defining frailty, odds of psychiatric illness increased (OR 1.23; 95% CI, 1.19-1.26). Similarly, psychiatric illness was associated with much higher odds of being among the most frail. These findings lend support to a multidimensional conceptualization of frailty. Our data also suggest that health care professionals who work with older adults with psychiatric illness should expect frailty to be common, and that those working with frail seniors should consider the possible co-existence of depression and psychiatric illness.