The excess risk refers to the excess rate of occurrence of a particular health effect associated with exposure to radiation.

Excess risks can depend on various factors including radiation dose, age at exposure, time since exposure, current age, and sex. Assessments of the risk among the atomic-bomb survivors are carried out using regression methods, and risk estimates are usually reported for a specific dose (often 1 gray or 1 sievert) for a specified combination of other important factors. In general, it is not possible to completely summarize the excess risk using a single number.

See also Excess relative risk, Excess absolute risk, Relative risk, and Absolute risk.