From October 2004 to September 2005, Radon222 activity inhigh-risk indoor spaces used by employees and students at theUniversity of Genoa was measured with CR-39 nuclear trackdetectors. The mean concentration in winter (78.9 Bq/m3 Â± 74.92 S.D.) was low in relation to the microenvironment considered. When data were broken down by type and location ofthe spaces, no significant differences were found, despite thefact that the Genoa conurbation lies on soil of variable geological composition. The dose absorbed by employees was 0.42 mSv/year, with a relative risk of 4.2/1000 cases of Radonrelated lung cancer. The dose absorbed by students was 0.28mSv/year, with a relative risk of 2.5/1000 cases of Radonrelated lung cancer. The level of radon activity detected neverexceeded the limit of 500 Bq/m3 established by Italian law.Nevertheless, the value of the compound uncertainty indexsuggested that the real level of Radon contamination couldhave exceeded 400 Bq/m3 in selected spaces, a value requiring annual concentration tests.