The rationale for, and establishment of, a computer-assisted, centralized immunization registry are described. This registry was created to improve the quality and quantity of information regarding immunization status for a defined population receiving primary care from a variety of providers, principally public clinics and private practitioners. An evaluation of the feasibility of the registry after one year's function shows that 93 per cent of eligible providers initially agreed to participate and 73 per cent continue to do so. Their reports have resulted in the creation of 17,500 individual patient files. Of a prospective cohort of newborns, 23 per cent were identified as "high-risk" for overdue immunizations. After one year, the immunization rates in audited groups improved significantly. The direct cost of this registry is less than 65 cents per currently registered child per year.