Catastrophic payments and fairness in financial contributions for health care are becoming increasing concerns for many governments. Out-of-pocket financing for health care is common in many developing countries, including Tanzania. As part of the Multi-Country Evaluation of the Integrated Management of Childhood Illness (MCE-IMCI), the objective of this paper is to explore the determinants of variation and the level of out-of-pocket payments for child health care in rural Tanzania, with and without IMCI, using data from two household surveys conducted in 1999 and 2002. We analyzed data for 833 visits to health providers for 764 children who had been sick in the 2 weeks prior to the survey and who had sought care at a 'Western' or formal health care provider. We found evidence that IMCI was associated with lower out-of-pocket costs at government facilities (Tshs.3.5 compared with Tshs.6.9 without IMCI) and in NGOs (Tshs.95.1 compared with Tshs.267.3). Out-of-pocket payments were on average Tshs.110.1 when care was sought at government primary health care facilities running a cost-sharing scheme, about 15 times higher than in those not part of the scheme (p<0.0001). Those who visited NGO facilities paid about 30 times more than those seeking care at government facilities not operating the cost-sharing scheme (p<0.0001). In conclusion, there is no doubt that health care financing mechanisms and equitable access to government facilities have a major impact on household economic burden related to under-five illness. Increasing access to IMCI-based care, however, offers an additional opportunity to reduce out-of-pocket payments, mainly through more rational use of medicines. Increasing access to IMCI-based care would not only improve inequities in financial contributions, but also in health, an important consideration for its own sake.