Polonium (Po-210) is the major contributor (with approximately 90%) to the radiation dose from radionuclides contained in the human diet, and it is mostly associated with seafood. This study presents Po-210 activity concentrations in the tissues of 16 fish species from the Aegean Sea and Sea of Marmara. Among all species investigated, the highest Po-210 activity concentration was 4450 & PLUSMN; 33 Bq kg(-1) dry weight (dw) in the digestive tract of anchovy (Engraulis encrasicolus), and the lowest Po-210 activity concentration was 1.3 & PLUSMN; 0.6 Bq kg(-1) (dw) in the muscle tissue of the thornback ray (Raja clavata). Significant differences in Po-210 concentrations were consistently found among the tissues of fish (P < 0.05). In general, the prominent accumulation of Po-210 was observed in the digestive tract and liver while the muscle tissue generally displayed the lower concentrations. Polonium concentrations in the internal organs, such as muscle and liver, were related to the feeding ecology of fish and thus are a consequence of Po-210 transfer in the food chain rather than Po-210 uptake from water. The average Po-210 concentration in fish filet was 54.1 Bq kg(-1) dw and to attain the recommended limit for the annual committed effective dose (1 mSv year(-1)) would require the consumption of 1024 kg of mixed fish filet in 1 year, which is unlikely to happen. The highest Po-210 activity concentration in the edible part of fish (filet) was determined in the anchovy (E. encrasicolus) but to reach the 1 mSv year(-1) limit would require still the consumption of 7.1 kg year(-1) of anchovy filet. Similar size specimens of wild and farmed fish, Dicentrarchus labrax and Sparus aurata, were analyzed to assess the differences in Po-210 concentrations. Polonium concentrations in the wild fish were several-fold higher than in farmed specimens, these ones fed with fish feed with Po-210 content lower than natural food in the sea. Therefore, the current trend of increasing the consumption of seafood from aquaculture seems to be reducing the radiation exposure to Po-210 in the human diet that is considered beneficial to public health.