In this study radon (222Rn) in indoor air was surveyed in 201 rooms of 26 major hospitals in Slovenia and annual effective doses for 1025 persons working in the rooms surveyed were estimated. Instantaneous radon concentrations were measured with alpha scintillation cells, long-term average concentrations with etched track detectors and electret detectors, and radon, its progeny and equilibrium factor were continuously recorded with portable devices. Effective doses were estimated by using ICRP Publication 65 methodology. Only in seven rooms did the average radon concentration, obtained by 1 month exposing etched track detectors, exceed the national limit of 400 Bq m-3; and these places will be mitigated; elsewhere it was lower. Annual effective doses for 966 persons (94.2%) were estimated as <1 mSv, but for 10 persons they were between 2.1 and 7.3 mSv. The results warn that in an environment with generally low radon levels, 'hot' points may be found, and therefore radon surveys should be carefully designed and performed in order not to miss them.