An on-line maternity data collection system has been designed to provide the information required for perinatal audit and to allow many of the letters and forms required for effective communication in pregnancy to be produced automatically. The system meets the requirements of the Korner Committee on Health Services Information and has been approved by the Computer Policy Committee. Pregnancy is followed prospectively from the first antenatal clinic visit until the file is closed 28 days after delivery. Data are entered by midwives and secretaries onto a network of microcomputers placed at convenient points in the maternity unit. The system has been fully operational with no significant problems since the beginning of 1984 and has led to improved communication between hospital and the community. Analysis of 253 consecutive case notes showed a high level of accuracy of the data recorded on computer. Reports and clinical audit are readily available both from the system locally, from standard programmes on the regional mainframe computer and via a mainframe computer at London University.