OBJECTIVE: To study the imaging features of patients with chronic ulcers of the leg that were associated with malignancy. DESIGN AND PATIENTS: All patients who on biopsy were proven to have malignancy--the majority of which were squamous cell carcinoma-were included in a prospective study. Ulcers limited to the foot were excluded but ulcers of the leg which extended into the foot were included. Amputation was performed in all but two patients, due to pain, bleeding or tissue necrosis. RESULTS: The etiology was multifactorial. The mean duration of the ulcers was 36 years including venous ulcers, extensive scarring of the leg secondary to infection, injury or burns. One ulcer was secondary to a snake bite. The remainder, usually in the upper part of the leg, had repeated episodes of blunt trauma or knife wounds, which were also complicated by infections which failed to heal or, if they healed, regularly recurred. Although arterial insufficiency was not primary in any patient, most were of advanced age and it may have been an element in some patients. Despite infection, osteomyelitis was present in only one patient. The essential features were bone destruction, soft tissue mass and periosteal reaction. The bone destruction was visible on the radiographs in all but one case. The soft tissue masses varied in size but in general were very large. The periosteal reaction varied in type but most commonly was lamellated. The classic undulating solid periosteal reaction of venous stasis was only occasionally present. The periosteal reaction was nonspecific in the majority of cases and did not aid in the diagnosis or etiology. MRI and CT studies were performed in six patients. These were helpful in defining the extent of bone destruction and periosteal reaction but were not essential in management. CONCLUSION: Chronic ulcer present for decades that then undergoes malignant change is a disease of developing countries where patients only consult physicians when they have developed complications such as pain, bleeding or tissue necrosis. Chronic ulcers may require to be biopsied at regular intervals as malignant change in these ulcers is directly related to their duration.