Abstract Background: Acute lipodermatosclerosis is characterized by pain and tenderness in the medial aspect of the leg. It is thought to be the result of venous insufficiency and to be the acute counterpart of chronic lipodermatosclerosis, a hallmark of venous disease. However, there is no direct evidence linking acute lipodermatosclerosis to venous disease. Objective: Our purpose was to determine whether acute lipodermatosclerosis is associated with venous insufficiency. Methods: With air plethysmography, we determined the venous filling index, the ejection fraction, and the residual volume fraction in 15 sequential patients with acute lipodermatosclerosis. Results: Ten of the 15 patients (67%) had at least one abnormal result, eight (53%) had two, and two (13%) had three. In four patients (27%), abnormalities of both reflux and ejection were noted. Duplex venous ultrasonography, in two of the patients with normal results from air plethysmography, showed incompetent perforators at sites of lipodermatosclerosis. Conclusion: Acute lipodermatosclerosis is associated with objective findings of venous insufficiency in a high percentage of patients. It is likely that this condition is the result of venous disease.