Reported here is a 46-year-old man who was seen for pain, numbness, and weakness in his left upper limb and hand. Electromyographic studies demonstrated denervation of ulnar-innervated muscle groups except for the flexor carpi ulnaris. A localized nerve conduction block could not be depicted because of severe axonal loss. Ultrasonographic evaluation showed enlargement of the ulnar nerve at 2 sites: at the level of the epicondylar groove and the inside of the flexor carpi ulnaris muscle. Herein, we would like to emphasize the complementary role of an ultrasound in peripheral nerve pathologies, not only does it confirm the entrapment but it also displays the underlying cause(s).