Although osteochondromas are common lesions, osteochondroma accompanying diastasis of the ankle joint in a child or adult is an uncommon condition. No previous cases of distal tibiofibular diastasis caused by an osteochondroma in adult have been reported except in child. The authurs experienced a case of mild distal tibiofibular diastasis secondary to an osteochondroma in a 37-year-old female presented with right ankle pain. Osteochondroma of the distal tibiofibular joint were detected on magnetic resonance imaging (MRI). She was pain-free 4 weeks after excision of the osteochondroma. The patient has remained asymptomatic for 1 years postoperatively. Early excision obviates the need for complex reconstructive surgery to correct ankle deformity later.