A 28-year-old submarine officer was involved in a dysbaric exposure at 155 feet for 21 hours. Subsequent to rescue, he developed a painful osteonecrosis involving over two-thirds of the femoral shaft and distal metaphysis. Pain is totally atypical for a bony injury of this distribution but because of failure to improve after 12 months, he underwent a series of three operations: (1) core biopsy, (2) intramedullary reaming and intramedullary rod fixation of the femur, and (3) bone grafting to a metaphyseal defect in the distal femur. Serial MRI scans were used to follow the progression of his osteonecrosis. This case report documents the first reported dysbaric diaphyseal osteonecrosis requiring surgery and intramedullary fixation to obtain a satisfactory clinical result.