Mucous cyst is a benign but recurrent lesion. It is located on the dorsal surface of the digital extremity between the distal interphalangeal joint and the base of the nail. The nail is often affected by the cyst because of its topographical proximity. Nail plate deformity may even be the first obvious abnormality indicating the presence of a small mucous cyst or subungual cyst. Mucous cyst is associated with osteoarthritis of the joint, osteophytes probably being the main contributing factor. Surgical treatment by joint debridement and cyst removal is the most effective way of preventing recurrence.