The aim of this study was to determine the correlation between fetal number and placentome diameters in pregnant sheep. In the present study 25 Kivircik mixed breed pregnant ewes were used. Pregnancy of the ewes was diagnosed by transrectal ultrasonography by the 25th day aft er insemination. A transabdominal probe (6.5 MHz) was used on the pregnant ewes at the 30th day. At this time the placentomes appeared as hypoechogenic areas with a "C"-like shape. Throughout the pregnancies 5 placentomes were measured from each ewe every week. The results showed no significant difference between placentome diameter size in single and twin-pregnant ewes except during the 5th and 12th weeks. The average of placentome diameter size in the single and twin-pregnant ewes was, respectively, 6.60 +/- 0.56 mm and 8.20 +/- 0.45 mm at the 5th week and 34.02 +/- 1.62 mm and 29.47 +/- 0.63 mm at the 12th week. The minimum significance degree was P < 0.05 in statistical analysis. This study found that measurement of placentome diameter size at the 5th and 12th week of pregnancy is not helpful in determining fetal number in a pregnant ewe. However, further investigations are needed to explain the difference in placentome diameter at the 5th and 12th weeks of pregnancy.