The aim of this study was to compare reported behavior in the sun in melanoma families with that of geographical healthy controls and to determine the predictors of that behavior to inform the process of counseling melanoma families. One hundred and seventy individuals with a family history of melanoma and 140 controls completed a postal questionnaire. Thirty-one percent of relatives reported sunburn in the previous summer, compared with 41% of controls. Fifty-five percent of relatives had acquired a suntan so that adherence to health education advice was disappointing. Male relatives were particularly likely to report sunburn. Higher knowledge scores correlated well with greater belief in ability to prevent melanoma, less desire for a tan, and more protective behaviors in relatives only (not in controls). We have shown that some psychological characteristics, sex, and age have an effect on behavior, so that the educational approaches needed will vary. "Better" behaviors were reported by melanoma cases than other relatives and by members of families with larger numbers of cases, which suggests that a belief that an individual is at particular risk of melanoma is important for compliance with preventive behaviors.