Active for Life After Cancer is a randomized trial evaluating the efficacy of a 6-month group-based lifestyle physical activity program (Lifestyle) for prostate cancer patients to improve quality of life (QOL) including physical and emotional functioning compared to a group-based Educational Support Program and a Standard Care Program (no group). A total of 134 prostate cancer patients receiving continuous androgen-ablation were randomly assigned to one of the three study conditions. Results indicated no significant improvements in QOL at 6 or 12 months. Both group-based programs were positively received and yielded good attendance and retention. Lifestyle participants demonstrated significant improvements in most theoretical mediators proposed by the Transtheoretical Model and Social Cognitive Theory to affect physical activity. Despite these improvements, no significant changes were found for most physical activity measures. Results suggest a lifestyle program focusing on cognitive-behavioral skills training alone is insufficient for promoting routine physical activity in these patients.