Possible causes of sacral and low back pain in the postpartum patient include sacroiliac joint dysfunction, sacroiliitis, lower lumbar diskitis, and irritation of the sciatic nerve. Postpartum stress fracture is a recognized cause of pain that should be considered in the differential diagnosis of the postpartum patient's low back pain. Several case reports of postpartum stress fracture are now in the literature (1, 2, 3, 4, 5, 6, 7, 8). A 30-year-old female presented postpartum with pain in the coccyx region that was most severe nine weeks after the uneventful spontaneous vaginal delivery of her first child. Imaging with computed tomography (CT) obtained 36 days after delivery demonstrated bilateral sclerosis in the lower sacrum. Plain film radiographs may not demonstrate this finding. Both magnetic resonance imaging (MRI) and CT are sensitive for sacral stress fracture.