Carpal coalition is an uncommon congenital abnormality that arises from incomplete cavitation of the common cartilaginous precursor that forms the carpal bones. When carpal coalition is discovered, it is typically an asymptomatic incidental radiographic finding, and is often bilateral. We present a case of symptomatic unilateral carpal coalition of the scaphotrapezial joint, which was treated by excising the fibrous coalition and placing an interposition fat graft. This treatment was effective in alleviating the patient's symptoms.