Although most countries have some type of private health insurance market (6), data on private insurance expenditures, populations covered, premiums charged and impact on the health care system, are very limited. This study uses data on private insurance available through National Health Accounts (see Appendix #1) which have several limitations: NHA data are not available for all countries and may underestimate the role of private insurance, particularly in developing countries where the private market tends to be unregulated; trend data for most developing countries is not reliable because reporting on private coverage is relatively recent. Also, since little systematic data have been collected on insurance markets in developing countries, evidence tends to be empirical and anecdotal. Despite these limitations, the increasing role of private insurance suggests that this topic needs greater attention. We hope that this paper will underscore the need to collect more extensive and reliable data in this area.