From the 13th century untill well into the 20th, the Habsburgs were one of the great powers in Europe--for most of this time, the leading dynasty. To preserve the purity of the line, marriages between uncles and nieces, aunts and nephews, and cousins were commonplace. As a consequence, genetic complexities developed, and the famous prognathic "Habsburg jaw," among other noticeable traits, was passed down to succeeding generations. Never has a dynasty been so well documented in paintings, and their portraits provide an unusually complete series of medical illustrations that show the facial characteristics that marked the family in general. The observations are confirmed and extended by information from modern medical sources as well as from the medical records that date to the Habsburgs' own times.