Transient osteoporosis of the hip (TOH) is a rare clinical condition with usually an unknown aetiology and which typically develops in middle-aged men, or in women in the third trimester of their pregnancy. It is characterized by transient osteopenia and by gradually increasing pain associated with a limitation of the range of motion of the hip. Bone marrow oedema is a typical but nonspecific finding in TOH. A 33-year-old female patient presented with severe hip pain one month after delivery. Her history was unremarkable except for a Hashimoto's Disease of 8 years' duration. Magnetic resonance imaging (MRI) showed significant bone marrow oedema with increased signal intensity in the femoral head on T2-weighted images. A diagnosis of TOH was made and the patient received a total of 30 sessions of hyperbaric oxygen (HBO) at 2.4 ATA, 2 hours each, in a multiplace chamber. Over the course of HBO treatment, her pain was gradually relieved and she became asymptomatic after one month together with a complete recovery of the range of motion of the hip. MRI of the hips 10 weeks after onset of HBO therapy showed normal signal intensity on T2-weighted images.