This study analysed the characteristics of respondent and nonrespondent mothers at each stage of a survey procedure, from a initial questionnaire to a reminder letter and two repeated mailings. Of 938 mothers of liveborn children who, while maternity inpatients, received a questionnaire and information about a mail survey to follow 2 months later, 828 completed and returned the initial questionnaire, 708 agreed to participate in the mail survey and were sent the mail questionnaire, and 612 finally completed and returned the questionnaire at 2 months. There were differences between respondents and non-respondents for socio-demographic factors at each stage of the process. The final response rate to the mail questionnaire was higher among mothers who were younger, were breast feeding, and had more education, an occupation and fewer children. The characteristics of late respondents were intermediate between those of early to middle respondents and nonrespondents for age, educational level, breast feeding and occupation. Maternal and infant health varied only slightly according to response status. Repeated mailings increased response and diminished selection. A mail questionnaire after contact in a maternity ward is a cost-effective means of gathering data about a large sample of recent mothers and their children.