The pyramidal lobe (PL) is a vestige of the embryonic thyroglossal duct and descends along with developing thyroid gland from the posterior third of the tongue to its ultimate position in the neck . PL can be delineated with ease using pinhole-collimator gamma camera imaging.5eeking the incidence and morphological characteristics of PL, we reviewed 200 consecutive cases of thyroid scintigrams performed during 2 years from March 1979 at the Department of Radiology , 5t. Mary'5 Hospital , Catholic Medica l College, 5eoul, Korea.There were 12 males and 188 females and the age ranged from 9 to 69 years. The scintigrams were either normal or d iffusely goitrous. Those with cold or hot nodules and poor images were not included.The results were as follows -1 . The incidence of PL was 104 (52 %) out of 200 cases , and PL was located in the left lobe of the gland in 50 (48. 1%), in the isthmus portion in 33 (3 1.7%) and in the right lobe in 21 (20 %). 2.PL was rod shaped in 57 cases (54.8 %), triangular or cone shaped in 42 (40.0 %) and dumbbell or club shaped in 5 (4.8 %). 3.The length of PL was 1 to 2 cm in 44 cases (42.3 %), 2 to 3 cm in 36 (34.6 %) and lessthan 1 cm in 11 (10 .4%) and more than 3 cm in 1 3 (12 .5 %). The width of PL was 0 .5 to 1 cm in 78 cases (75 %), less than 0.5 cm in 12 (11.5 %) and more than 1 cm in 14 (13.5 %). 4.To evaluate the histopathologic relationship between the thyroid gland proper and PL , we measured the length of PL in 54 cases of normal group and in 21 cases with diffuse goiter , retrospectively.The mean and strandard deviation in the former was 1.64 :t 0.66 cm and in the latter 1.77 :t 0 .6 7cm.The d ifference between the normal and goitrous group was not significant statistically suggesting that the biological behaviour of PL is probably parallel to that of the thyroid gland proper.