De Quervain's disease is a painful tenosynovitis of the abductor pollicis longus and extensor pollicis brevis muscle tendons located in the first dorsal compartment. The primary treatment for De Quervain's disease is conservative; surgical intervention is rarely required. Currently, there is no standardized treatment protocol supported by strong, up-to-date evidence. The aim of this study is to compare the effectiveness of a static hand-wrist resting splint and exercise therapy in the conservative treatment of De Quervain's tenosynovitis. Patients will be evaluated in terms of pain levels, functional/symptom status, hand-finger strength, pressure pain threshold (PPT), tendon cross-sectional area measured by ultrasound, and the presence of effusion findings (semiquantitative; 0-3), and patient satisfaction.