Tennis leg, strain of the medial head of the gastrocnemius muscle, may follow a trivial trauma in athletic and nonathletic activities. Complete or partial tears of the musculotendinous unit may result in a hematoma. Clinical manifestations of gastrocnemius hematoma in a 64-year-old man with local swelling, pain and tenderness that was aggravated by passive dorsiflexion of the ankle joint, mimicked deep vein thrombosis. Failure to appreciate the precedent trivial trauma and the localized swelling and ecchymosis led to delayed diagnosis and inappropriate heparinization. The definite diagnosis was established by CT scan which revealed a local soft tissue mass within the gastrocnemius consistent with a hematoma. A compartment syndrome developed the day after heparinization and was adequately treated by discontinuation of heparin, aspiration and rest. Differentiation between tennis leg and deep vein thrombosis is of paramount importance, since the etiology, treatment and prognosis of these two clinical entities are quite different. Venography is recommended as specifically diagnostic for deep vein thrombosis while CT scan for gastrocnemius hematoma.