Carpal tunnel syndrome is typically diagnosed from history and physical examination then confirmed with electrodiagnosis. Electrodiagnosis provides only limited anatomic information and evaluation of space-occupying lesions. The authors present two cases in which demonstrated flexor pollicis longus tenosynovitis coexistent with carpal tunnel syndrome was diagnosed with ultrasonography. Ultrasonography is an effective modality that enhances the investigation of diseases in the soft tissues of the wrist and the hand. It can be useful in directing specific treatment by increasing diagnostic accuracy.