A follow-up study at 3 months shows resolution of most of the bone edema. Transient osteoporosis is a self-limiting disease of unknown etiology. It occurs in middle-aged males and females in late pregnancy typically. The hip is the most common joint affected. There is rapid-onset hip pain associated with demineralization, usually unilateral. MRI findings are of diffuse marrow edema and a small joint effusion. Bone scans show increased uptake. Spontaneous recovery occurs within 2-6 months. The differential diagnosis includes avascular necrosis, metastases, and reflex sympathetic dystrophy. Evidence of subchondral bone collapse, serpiginous subchondral interface, or cold spots on bone scan should prompt a diagnosis of AVN rather than transient osteoporosis.