The efficacy of lymphoscintigraphy in the diagnosis of lymphedema was evaluated in 17 patients (total of 20 extremities). Final diagnoses were: three extremities with primary lymphedema, eight with secondary lymphedema, and nine with edema due to other causes. Qualitative interpretation of image patterns was reliable in differentiating lymphedema from edema of other origins (sensitivity 73%, specificity 100%). There were eight true-positive, nine true-negative, no false-positive, and three false-negative extremities. The three false-negative results occurred in extremities that were not imaged within the first hour. Lymphoscintigraphy is a reliable, objective, and noninvasive means of supporting the diagnosis of lymphedema, and lends itself more readily to repeated studies for follow-up than other available tests.