Among 1000 patients, 219 had seriously harmed themselves through the abuse of tobacco, alcohol, food, or drugs. Of these, 25% complied with treatment advice and corrected the abuse. Cooperation, when obtained, was prompt, whereas repeated counseling was ineffective. The follow-up period averaged 4.9 years. Men outnumbered women and were more compliant. Compliance related poorly to socioeconomic status and education but was greater in stable than in unstable personalities. Habits were reinforced by social custom, habituation, psychologic and physiologic dependency, pleasure, perversity, and style of living. Results from other studies are similarly poor. Improving health behavior lies generally outside medicine proper. Physicians have a pivotal responsibility for guiding patients toward health but have a limited voice in improving patients' health habits.