Proponents of user fees in the health sector in poor countries cite a number of often interrelated rationales, relating inter alia to cost recovery, improved equity and greater efficiency. Opponents argue that dramatic and sustained decreases in service utilization follow the introduction of user fees, highlighting evidence that user fees reduce service utilization when they fail to result in improved quality of care and/or when services are priced higher than those charged by private health care providers. Utilization of public health services in Cambodia is low. Supply-side factors are significant determinants of such low public sector utilization, including low official salaries of service providers (forcing many to seek additional income in the private sector), and operations budgets which are erratic and often insufficient to cover running costs of service delivery outlets. The Cambodia Ministry of Health (MOH) encourages user fee schemes at operational district level. By allowing revenue to be retained at the health facility level, the MOH aims to improve health care delivery--and consequently service utilization--through increased salaries to health facility staff and increases in operations budgets. This case study of the introduction of user fees at a district referral hospital in Kirivong Operational District in Cambodia, using the findings from empirical research, examines the impact of user fees on health-careseeking behaviour, ability to pay and consultation prices at private practitioners. The research showed that consultation fees charged by private providers increased in tandem with price increases introduced at the referral hospital. It further demonstrates--for the first time that we are aware of from the available literature--that the introduction and subsequent increase in user fees created a 'medical poverty trap', which has significant health and livelihood impact (including untreated morbidity and long-term impoverishment). Addressing the medical poverty trap will require two interventions to be implemented immediately: regulation of the private sector, and reimbursing health facilities for services provided to patients who are exempted from paying user fees because of poverty. A third, longer-term initiative is also suggested: the establishment of a social health insurance mechanism.