OBJECTIVE AND IMPORTANCE: Median nerve neuropathy can be clinically devastating to a patient. It can be caused by compression of the median nerve anywhere along its course. We present the case of delayed median nerve neuropathy after the placement of a vascular graft in the arm. CLINICAL PRESENTATION: An arm shunt was placed in the nondominant upper extremity in a 60-year-old man with end-stage renal disease. Twelve hours postoperatively, the patient developed neurapraxia in the median nerve distribution in the hand. INTERVENTION: Exploration of the arm revealed a lipoma coursing along and deep to the median nerve. Resection of the lipoma decompressed the nerve. CONCLUSION: In this patient, median nerve neuropathy was caused by a lipoma and postoperative swelling from placement of the vascular graft. The swelling that occurred after the shunt placement unmasked subclinical compression of the nerve by a lipoma deep to the median nerve. To our knowledge, this report is unique in documenting damage to the median nerve after vascular graft placement as a result of an occult mass.