The 1983 US Orphan Drug Act has stimulated the development of new therapies for rare diseases. To provide the first comprehensive overview of orphan-designated products and their indications, this article quantitatively analyses the characteristics and distribution of orphan designations and approvals by the US Food and Drug Administration from 1983 to August 2008. Of the 1,892 orphan-designated products, 326 received marketing approval, representing 247 different drugs and more than 200 different diseases. About half of the approvals had occurred by 4 years after designation was granted. The most common patient population size for orphan designations and approvals was fewer than 10,000 patients, and cancer was the most common disease area. The implications of such findings for future development and marketing of therapies for rare diseases are discussed.