The pyramidal lobe (PL) is a vestige of the embryonic thyroglossal duct and descends along with developingthyroid gland from the posterior third of the tongue to its ultimate position in the neck. PL can be delineatedwith ease using pinhole-collimator gamma camera imaging. Seeking the incidence and morphological charactesitics ofPL, we reviewed 200 consecutive cases of thyroid scintigrams performed during 2 years from March 1979 at the Dept.of Radiology, St. Mary's Hospital, Catholic Medical College, Seoul, Korea. There were 12 males and 188 females andthe age ranged from 9 to 69 years. The scintigrams were either normal or diffusely goitrous. Those with cold orhot 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 in33(31.75) and in the right lobe in 21(20%). 2. PL was rod shaped in 57 cases (54.8%), traiangular or cone shapedin 42(40.0%) and dumbbell of club shaped in 5(4.8%) 3. The length of PL was 1 to 2cm in 44 cases (42.3%), 2 to 3cmin 36(34.6%) and les than 1cm in 11(10.4%) and more than 3cm in 13(12.5%). The width of PL was 0.5 to 1cm in 78cases (75%), less than 0.5cm in 12(11.5%) and more than 1cm 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 wasnot significant statistically suggesting that the biological behaviour of PL is probably parallel to that of thethyroid gland proper.