Flexor hallucis longus tendinitis is a common overuse syndrome in classic ballet dancers. To describe the clinical symptoms, diagnosis and non-operative and operative treatment, we evaluated twenty ballet dancers from march 1994 to August 1995. For the diagnosis, Tomasen test was helpful clinically and MRI was essential for surgical intervetion to find a tendon degeneration. Patients were classified into three groups by symptoms and clinical stages. All of the Group 1 and 2 were recovered by means of the conservative treatment. Two dancers belongs to Group 3 showed a severe degeneration of tendon on the MRI scan, finally was taken the an operation. Release of the tarsal tunnel were performed. Six months after operation, they could return to dancing.