This is the first of series of articles which describes an integrated system for recording medical data. The age-sex register is described in detail. Uses of the register include enhanced capabilities for office management, assessment of postgraduate educational needs, outreach, audit, and research. The problems encountered with definition of the practice size are discussed. Subsequent articles will describe a classification of health problems, a diagnostic index, family folders, filing patients records by geographic location, problem-oriented medical records, encounter forms, and various record forms.