In contrast to radicular pain during pregnancy, the incidence of postpartum radicular pain is rare. Sacral stress fractures are unusual but important causes for low-back and buttock pain and even postpartum radicular pain. To date, only 10 postpartum sacral stress fractures have been reported in the literature, with two descriptions of radicular pain as the presenting symptom. A 36-year-old woman, 7 days after her second delivery, presented with symptoms of spontaneous acute claudicating in conjunction with a left-leg radicular pain for 5 days. Imaging studies revealed a left sacral stress fracture. Bone mineral density was normal. The patient reported no pelvic, back, or radicular pain during the pregnancy, and had no history of menstrual irregularities, previous fracture, eating disorder, trauma or endocrine or metabolic diseases. No smoking or use of anticoagulation drugs was reported. Her obstetric and labor history showed no other risk factors. Epidural analgesia was used. Treatment consisted of toe-touch walking with crutches for 2 months, followed by full weight bearing, which resolved nearly all her symptoms. Clinicians should consider sacral fracture as a diagnostic possibility in postpartum and pregnant patients with lower back and/or buttock pain with or without radicular pain. Bone scintigraphy and computed tomography are considered harmful for the fetus. Magnetic resonance imaging, which is more suitable for pregnancy, is more sensitive than bone scintigraphy in revealing stress injuries of the bone. Physical examination and proper radiologic evaluation are the main keys for revealing the pathology.