Muscle herniation in the upper extremity is a rare but recognized phenomenon with a paucity of reports in the current literature. In the majority of cases, the herniation is secondary to trauma, with some of the cases due to muscle hypertrophy and increased intra-compartmental pressure from the forced exertion. Treatment for this condition ranges from nonsurgical, repair, or reconstruction to fasciotomy of the flexor carpi ulnaris fascia. Here, we present a case of flexor carpi ulnaris herniation after an open in situ cubital tunnel release in a 57-year-old male 6 years after initial surgery. The patient's symptoms did not improve with conservative management, and the patient subsequently underwent endoscopic fasciotomy with resolution of his symptoms and maintenance of his wrist and grip strength. The rationale for the treatment chosen is discussed.