Canadian family physicians were sent questionnaires that asked how they would handle the ethical problems posed by six sample cases and what reasons were relevant to their decisions. The ethical problems concerned how much information to divulge to patients, how extensively a physician should become involved in the lifestyles of patients and how to deal with a possible family problem. The study identified characteristics of family physicians that affect their ethical decision making and tested a theoretical model that regards ethical problems as conflicts between respecting patient autonomy and promoting patient welfare. The varied responses suggested that ethical issues are resolved on a case-by-case, rather than a theoretical, basis. Certification in family medicine was the only characteristic associated with a consistent pattern of responses; certificants were more likely than other physicians to involve patients in decisions.