Background: In the last decades, there has been increased worldwide interest in the management of healthrisks from indoor radon.Methods: From 2006 to 2008, a survey on air radon levels was carried out in a total of 57 indoor gymnasiarespectively located in the urban area of Palermo (Sicily) and Sassari (Sardinia).Results: The indoor radon levels were generally low with different geometric means in the two geographicareas (14.3 Bq/m3 in Palermo and 36 Bq/m3 in Sassari, respectively). Overall, in both groups increasingvalues of radon were found during the night and the early morning, with radon concentrations significantlylower during working time than at other times. The analysis of structural parameters showed that directcontact with the soil significantly correlated with increased levels of radon in gymnasia located in Palermo’sarea (p<0.05). Furthermore, higher radon levels in Sicilian structures were also associated, although notsignificantly, with lack of sumps (19.3 vs 12.9 Bq/m3), location below the ground level (18.8 vs 8.7 Bq/m3),lack of windows (25 vs 13.2 Bq/m3), presence of forced ventilation (15.5 vs 7.3 Bq/m3) and with cracks ormoisture tracks (15.7 vs 13.2 Bq/m3).Conclusions: Radon tends to accumulate in indoor sites and it’s monitoring, especially in buildings withpotentially overcrowded conditions, could be of public health interest. Mitigation measures and minimizationof the number of structural and functional risk parameters should be strongly encouraged in order to limitradon accumulation especially in countries with higher radium concentration in the soil.