Lipoedema is a common but infrequently recognized condition causing bilateral enlargement of the legs in women. Although generally considered to be the result of an abnormal deposition of subcutaneous fat with associated oedema, the precise mechanisms responsible for oedema formation have yet to be fully established. In order to evaluate the possible role of lymphatic or venous dysfunction in the pathogenesis of lipoedema, 10 patients were investigated by photoplethysmography (venous function) and quantitative lymphoscintigraphy (lymphatic function). The results were compared with those from patients with primary lymphoedema and those from healthy volunteers. The results demonstrated minor abnormalities of venous function in only two patients. One patient had moderately impaired lymphatic function in both legs and seven patients had a marginal degree of impairment in one or both legs. However, in none of these cases did the impairment attain the low levels seen in true lymphoedema. Lipoedema appears to be a distinct clinical entity best classified as a lipodystrophy rather than a direct consequence of any primary venous or lymphatic insufficiency.