BJECTIVES Thyroid gland volume may vary physiologically during pregnancy and lactation. We aimed to determine ultrasonographic changes in thyroid volume in this study.MATERIALS AND METHODS The thyroid ultrasound in 30 mothers was performed at the 9th months of gestation, and also 6th and 12th months after delivery, to calculate thyroid volume. The volume of each lobe was estimated in cubic centimeters using the equation of Brunn et al. The volume of each thyroid gland was obtained by collecting the volume of the right and left lobes. The data were analyzed using SPSS, version 15.0 package program.RESULTS The mean volume of the thyroid gland in women in the control group was 11.95 ± 1.90 mL. When compared with the control group, a significant increase in thyroid gland volume was seen in the third trimester. Decrease at the sixth month after delivery was not significant. But the decline in the values in the twelfth month was statistically significant.CONCLUSION Knowing the limits of this physiological increase will be important in distinguishing it from other possible pathologies. We think that the mean thyroid volume values we find will be useful in daily clinical practice.