Hereditary osteo-onychodysplasia, also known as the nail-patella syndrome (NPS), consists of a clinical tetrad of nail dysplasia, hypoplastic or absent patella, radial head dislocation, and iliac horns. Bilateral posterior iliac horns are observed only in NPS and present in >80% of patients. We describe the appearance, location, and structure of iliac horns by CT, MRI, and 3-dimensional CT reconstruction.