A written questionnaire suitable for obtaining comprehensive genetic family data was developed. The questionnaire was designed to solicit information on the name, date of birth, sex, health problems, date of death (if deceased), spouse, abortions, stillbirths, and offspring of the patient plus first, second, and some third degree relatives of the patient. The questionnaire was evaluated for its effectiveness in obtaining an accurate and complete family history. During the first phase, 77 completed questionnaires were continuously assessed, and the questionnaire was modified until the present version evolved. Using the present version, 60 completed questionnaires disclosed only 15 problems, 10 of them minor. The questionnaire was also designed in conjunction with a computer programme developed for the entry of pedigree data. This programme is part of the computer system, MEGADATS, which is used for the acquisition, storage, and manipulation of genetic family data. The questionnaire offers these advantages over the pedigree obtained at the time of the clinic visit: (1) permits consultation with other family members, (2) saves clinic time, (3) gives prior knowledge of reason for clinic appointment, (4) anamnestic infallibility, (5) time is available to check for family record linkage, (6) computer adaptability for entering pedigree data, and (7) basic format can be modified easily. A modified sample questionnaire is presented in the Appendix.