Lymphoscintigraphy (LS), performed with technetium 99m-labeled antimony trisulfide colloid (Cadema Medical Products, Inc., Middletown, N.Y.), was used as a noninvasive diagnostic examination to evaluate the lymphatic circulation in 190 extremities of 115 patients. Forty-six patients had primary lymphedema, 48 had secondary lymphedema, and 21 patients had other causes of limb swelling. To determine the value of LS in surgical decision making, preoperative and postoperative LS of 16 patients who underwent surgical repair of the lymphatic abnormality were studied separately. Semiquantitative evaluation of the lymphatic drainage and visual interpretation of the image patterns were reliable to differentiate lymphedema from edemas of other origin (sensitivity: 92%, specificity: 100%). Although certain image patterns were characteristic of either primary or secondary lymphedema, LS could not consistently differentiate between the two types. Episodes of cellulitis in lymphedema clearly delayed lymph transport. LS was helpful in patient selection and follow-up after lymphatic surgery, but it did not prove patency of lymphovenous anastomoses. It was diagnostic in the evaluation of lymphangiectasia and was used to document successful surgical treatment of reflux of chyle. LS is safe and reliable and has no side effects. It should replace contrast lymphangiography in the routine evaluation of the swollen extremity.