Physicians who care for children can and should help patients avoid the use of tobacco. Physicians are well aware of the health hazards associated with tobacco use, inasmuch as smoking is the chief, single cause of premature mortality in this country. Each day, more than 3000 children in the United States begin to use tobacco. Physicians who care for children have patients at vastly different stages of intellectual and social maturity. Both the theory and practical details of tobacco-related interventions differ among infants, children, and adolescents. The physician is in a unique position to intervene in the early stages. Anticipatory guidance--the practice of providing counsel regarding potential problems--is a key part of health care for the young. If physicians provide messages about tobacco use that are appropriate to the patient's age and developmental stage, the potential for broad public health impact is great. Based on a series of clinical trials, the National Cancer Institute developed a manual to assist physicians in helping their patients stop smoking. The recommendations in this manual include four physician activities that begin with the letter A (four A's): Ask, Advise, Assist, and Arrange follow-up. For physicians who treat children, a fifth A, Anticipatory guidance, is added.