Objective There is very little research on patient organizations (POs), even though their numbers and influence seem to be increasing. The purpose of this study was to describe the establishment, membership, size, organization, decision making and basic funding of national POs in Finland.Setting and participants National POs (n = 130) were identified from their umbrella organizations and by Internet searches. Data were collected from POsÕ web pages (87% of POs had one), FinlandÕs Slot Machine Association (RAY, an important public financier of POs), a relevant survey done by a local TV-company, and interviews and written materials of POs.Results and conclusions Some current national POs were established around the turn of the 19 th century. The rate of establishment of new POs increased from the 1970s and particularly in the 1990s when POs were characterized by increasing specialization. POs focused on different patient groups and diseases and were founded by philanthropists, physicians, patients, parents and the drug industry. Members could be patients, patient relatives, health-care professionals and organizations. POs widely varied in memberships (20-145 000, in 2002) and in number of paid personnel (0-1395, in 2002), organizational structure and decision making. Interest groups and financiers were often represented in decision-making organs. Activities included mutual support and service production, and, increasingly, informing and lobbying. POs had wide domestic and international co-operation and networking. Drug industry marketing was visible on PO web pages. Budget sizes varied (4000-15 million euros, in 2001). The main public financier was RAY. The old national POs were large and part of national social and health care, but newer ones were often established for mutual support and lobbying. National POs are not uniform but characterized by great variation. The number of national POs is increasing suggesting tighter competition for financing and visibility in the future.