The relationship among age, comorbidity, and physical activity have been relatively understudied among breast, colorectal, and prostate cancer populations despite their known impact on morbidity and mortality. In this article, we review evidence supporting the efficacy of physical activity interventions in improving cardiovascular risk groups, the elderly and cancer patients. Preliminary studies conducted with older patients suggest that physical activity interventions can reduce fatigue, elevate mood, improve physical functioning, reduce physical, role limitations, decrease falls, attenuate losses in bone density, promote weight loss, and modify CHD risk factors. Although relatively few randomized clinical trials have assessed the efficacy of physical activity interventions in cancer patients, the research suggests that these interventions can have both physical and mental health benefits. The implications and limitations of these findings are discussed. Further studies that use larger sample sizes and examine possible moderating variables, such as age, on the efficacy of such interventions are needed.