[en] It has been reported that not only health effects directly induced by radiation exposure but political, economic and social effects were caused in various ways by the Chernobyl accident. Taking account of significance of these indirect effects of events with radiation exposure, risk assessment for radiation protection should be performed on the basis of more comprehensive index of detriments. Relative magnitude of miseries which people perceive could be useful for an unified index of harm. Because magnitude of miseries due to different harmful events depends on personal sense of values and perception, it is necessary to use average value of the magnitude which are examined with investigation by questionnaires. There is a large uncertainty in estimating risks from exposure to low level radiation. If a risk from some radiation exposure is possibly over estimated in order to take safety side for radiation protection, a risk from other serious risk sources could be misesteemed. Therefore these uncertainties should be considered appropriately in comparing risk for decision making. For example, effect of indoor radon was estimated to be more serious than other natural radiation sources in spite of large uncertainties in estimating risk. From such points of view, the problems in a risk assessment for radiation protection were discussed. (author)