BACKGROUND: Older cancer survivors are at increased risk for secondary cancers, cardiovascular disease, obesity, and functional decline and, thus, may benefit from health-related interventions. However, to the authors' knowledge, little is known regarding the health behaviors of older cancer survivors and the associations of those behaviors with quality-of-life outcomes, especially during the long-term post-treatment period. METHODS: In total, 753 older (aged > or =65 years) long-term survivors (> or =5 years postdiagnosis) of breast, prostate, and colorectal cancer completed 2 baseline telephone interviews to assess their eligibility for a diet and exercise intervention trial. The interviews assessed exercise, diet, weight status, and quality of life. RESULTS: Older cancer survivors reported a median of 10 minutes of moderate-to-vigorous exercise per week, and only 7% had Healthy Eating Index scores >80 (indicative of healthful eating habits relative to national guidelines). Despite their suboptimal health behaviors, survivors reported mental and physical quality of life that exceeded age-related norms. Greater exercise and better diet quality were associated with better physical quality-of-life outcomes (eg, better vitality and physical functioning; P < .05), whereas greater body mass index was associated with reduced physical quality of life (P < .001). CONCLUSIONS: The current results indicated a high prevalence of suboptimal health behaviors among older, long-term survivors of breast, prostate, and colorectal cancer who were interested in lifestyle modification. In addition, the findings pointed to the potential negative impact of obesity and the positive impact of physical activity and a healthy diet on physical quality of life in this population.