Self-reports of disease from relatives are generally believed to be more detailed than those received from a family informant, although differential participation may exist among the relatives who provide information. To investigate the potential for differential participation, we requested permission to contact relatives of mothers (informants) who had provided family history information for a population-based case-control study of orofacial clefts. Birth defect and cancer self-reports were received from 345 (65.6%) case and 380 (68.8%) control relatives. Participants and nonparticipants differed little by type (maternal or paternal) or degree of relationship. Informants, however, were more likely to permit contact with relatives who were maternal, first-degree and female. Relatives appeared willing to provide self-reports, although the potential for differential selection introduced by informants should be considered.