Differences in coping by 105 aging mothers of adults with mental illness and 389 similar mothers of adults with mental retardation were investigated. Although no differences in problem-focused coping were found, mothers of adults with mental illness used more emotion-focused coping, which predicted greater maternal depression. For mothers of adults with retardation, depressive symptoms were a function of their child's behavior problems, although this source of stress was buffered by coping. For mothers of adults with mental illness, depression was a function of caregiving demands, but coping did not buffer the effects of stress. Explanations for findings include maternal perceptions of the context of care, of her control over the disability, and her caregiving efficacy.