In Bangladesh, there is a lack of knowledge about the large body of informal sector practitioners, who are the major providers of health care to the poor, especially in rural areas, knowledge which is essential for designing a need-based, pro-poor health system. This paper addresses this gap by presenting descriptive data on their professional background including knowledge and practices on common illnesses and conditions from a nationwide, population-based health-care provider survey undertaken in 2007. The traditional healers (43%), traditional birth attendants (TBAs, 22%), and unqualified allopathic providers (village doctors and drug sellers, 16%) emerged as major providers in the health care scenario of Bangladesh. Community health workers (CHWs) comprised about 7% of the providers. The TBAs/traditional healers had <5 years of schooling on average compared with 10 years for the others. The TBAs/traditional healers were professionally more experienced (average 18 years) than the unqualified allopaths (average 12 years) and CHWs (average 8 years). Their main routes of entry into the profession were apprenticeship and inheritance (traditional healers, TBAs, drug sellers), and short training (village doctors) of few weeks to a few months from semi-formal, unregulated private institutions. Their professional knowledge base was not at a level necessary for providing basic curative services with minimum acceptable quality of care. The CHWs trained by the NGOs (46%) were relatively better in the rational use of drugs (e.g. use of antibiotics) than the unqualified allopathic providers. It is essential that the public sector, instead of ignoring, recognize the importance of the informal providers for the health care of the poor. Consequently, their capacity should be developed through training, supportive supervision and regulatory measures so as to accommodate them in the mainstream health system until constraints on the supply of qualified and motivated health care providers into the system can be alleviated.