Transient osteoporosis of the hip (TOH) is an unusual self-limiting skeletal disorder of unknown etiology, characterized by pain in the hip and radiographic osteopenia of the femoral head and neck. TOH usually occurs during the third trimester of pregnancy. It was first described by Curtiss and Kincaid in 1959 [1], and Lequesne [2] coined the term “transient osteoporosis” in 1968. To our knowledge, there are no data on the incidence of TOH during pregnancy and the early postpartum period [3]. Its clinical diagnosis can be difficult and the symptoms are often initially misinterpreted. Pathologic fracture is considered to be the most serious complication of this disorder. A 29-year-old, gravida 1, para 0, Caucasian woman was admitted to hospital at 40 weeks’ gestation for amniorrhexis. She had no medical history of hyperthyroidism, Cushing syndrome, liver or renal disease, and no history of corticosteroid, anticonvulsant or anticoagulant therapy. She was a non-smoker. There had been no recent episode of trauma. The pregnancy had been correctly controlled. For 4 weeks previously, the patient had experienced gradually increasing pain in the left buttock, groin and thigh, radiating to the left knee. These symptoms were present when the patient was at rest and were exacerbated by activity. Ten hours after admittance, an instrumental vaginal birth by vacuum extraction was performed under epidural analgesia. This was shortly followed by the development of more severe pain in the left hip during the early postpartum period. The patient weighed 99 kg and was 172 cm tall. The left leg appeared shortened and externally rotated. Active and passive ranges of motion of the hip were decreased with functional disability. The Lasegue test was negative and the left rotulian reflex was decreased. The results of full blood count, sedimentation rate, calcium phosphate, alkaline phosphatase, liver function tests and renal function tests were normal. An anteroposterior radiograph of the pelvis revealed a completely displaced subcapital fracture of the left femur with osteopenia of the proximal part of the femur from the lesser trochanter proximally (Figure 1). External traction was applied until definitive surgical treatment was performed. The patient underwent a cementless total hip arthroplasty 2 months after delivery. Histopathologic studies revealed osteoporotic signs with regressive and reparative areas in the femoral head. The patient was given a calcium and vitamin D (400 IU) supplement twice a day and bisphosphonates once a week. The clinical and radiologic evolutions were satisfactory. Radiographs of the hip 6 months postoperatively showed a correctly placed prosthesis (Figure 2), and the patient was walking without a limp 9 months after delivery. Transient osteoporosis is a self-limiting syndrome that can affect men and women during the fourth or fifth decade of life, but is more frequent in women during the last trimester of pregnancy. Two-thirds of cases appear in primiparas [3]. It usually affects the hips (76%) and, rarely, the knees, ankles or feet [4].