There is currently considerable discussion between governments, international agencies, bilateral donors and advocacy groups on whether user fees levied at government health facilities in poor countries should be abolished. It is claimed that this would lead to greater access for the poor and reduce the risks of catastrophic health expenditures if all other factors remained constant, though other factors rarely remain constant in practice. Accordingly, it is important to understand what has actually happened when user fees have been abolished, and why. All fees at first level government health facilities in Uganda were removed in March 2001. This study explores the impact on health service utilization and catastrophic health expenditures using data from National Household Surveys undertaken in 1997, 2000 and 2003. Utilization increased for the non-poor, but at a lower rate than it had in the period immediately before fees were abolished. Utilization among the poor increased much more rapidly after the abolition of fees than beforehand. Unexpectedly, the incidence of catastrophic health expenditure among the poor did not fall. The most likely explanation is that frequent unavailability of drugs at government facilities after 2001 forced patients to purchase from private pharmacies. Informal payments to health workers may also have increased to offset the lost revenue from fees. Countries thinking of removing user charges should first examine what types of activities and inputs at the facility level are funded from the revenue collected by fees, and then develop mechanisms to ensure that these activities can be sustained subsequently.