The consequences for public sector medical care of the introduction of medical insurance into New Zealand are traced. The analysis is based on a simple choice model describing consumer decisions and their consequences; it is elaborated by data drawn from government records, survey interviews with insured and uninsured groups and mail questionnaire responses from politicians. It is argued that the ultimate consequence of the introduction of medical insurance is the destruction of welfare state arrangements for the provision of medical care. The thesis concludes with the formulation of a proposal likely to prevent this.