Although user fees are a common form of healthcare financing in resource-poor countries, there is growing consensus that their use compromises health service utilisation and population health. Between 2003 and 2006, Médecins sans Frontières (MSF) conducted population-based surveys in Burundi, Sierra Leone, Democratic Republic of Congo, Chad, Haiti and Mali to determine the impact of user fees on healthcare-seeking behaviour and access. For general and disease-specific conditions, MSF also measured the impact of (i) reduced payment systems in Chad, Mali, Haiti and Burundi and (ii) user fee abolition for certain population groups in Burundi and Mali. User fees were found to result in low utilisation of public health facilities, exclusion from health care and exacerbation of impoverishment, forcing many to seek alternative care. Financial barriers affected 30-60% of people requiring health care. Exemption systems targeting vulnerable individuals proved ineffective, benefiting only 1-3.5% of populations. Alternative payment systems, requiring 'modest' fees from users (e.g. low flat fees), did not adequately improve coverage of essential health needs, especially for the poorest and most vulnerable. Conversely, user fee abolition for large population groups led to rapid increases in utilisation of health services and coverage of essential healthcare needs. Abolition of user fees appears crucial in helping to reduce existing barriers to health care. The challenge for health authorities and donor agencies is around working creatively to remove the fees while addressing the financial consequences of improved access and providing quality care.