An os trigonum is a small, round bone situated just behind the ankle joint. Clinical research shows that the os trigonum is present in about 5-15 % of normal feet. It occurs when one part of the bone does not fuse with the rest of the talus during growth. The present study is made on the skeletons, which were found in the Karagunduz, Dilkaya and Van Kalesi-Eski Van Sehri settlements, Van province, Anatolia, dated in the Middle Ages. In this study 228 skeletons were examined, 120 males and 108 females. 376 tali were studied: 227 from Karagundbuz, 93 from Dilkaya, and 56 from Van Kalesi-Eski Van Sehri. The percentage of the os trigonum syndrome was recorded as 6.6 %.