Indoor radon concentrations are subject to seasonal variation, which directly depends on weather conditions. The seasonal indoor radon concentrations were measured and the annual effective dose was estimated for the city centre of Eskisehir, Turkey. In order to reflect annual averages measurements were performed over all seasons (winter, spring, summer and autumn) including also the entire year. Measurements were carried out using Kodak-Pathe LR 115 Type II passive alpha track detectors in 220 different houses. A total of 534 measurements including measurements of different seasons were taken between 2010 and 2011. The radon concentrations for winter ranged from 34 to 531 Bq m(-3), for spring ranged from 22 to 424 Bq m(-3), for summer ranged from 25 to 320 Bq m(-3), and for autumn ranged from 19 to 412 Bq m(-3). Yearly measurements ranged from 19 to 338 Bq m(-3). In this study the average annual effective total dose from radon and its decay products was calculated to be 3.398 mSv y(-1).