The extensive enlargement of a solitary osteochondroma in a skeletally mature patient is rare and might result from malignant transformation. Excision of such a lesion in the distal and lateral aspect of the tibia is difficult because of the risk of injury to the neurovascular structures and the possible functional consequences with respect to ankle stability. We present a case of an active osteochondroma arising from the posterolateral distal tibia in an adult patient. The tumor was successfully excised by using a transfibular approach with fibular reconstruction. No signs of recurrence were noted 2 years after surgery.