Mandibular prognathism is a disfiguring, genetic disorder where the lower jaw outgrows the upper.

The condition is colloquially referred to as Habsburg jaw or Habsburg lip (see Habsburg) due to its prevalence in that bloodline.

Royalty with the condition

• Charles II of Spain suffered from the condition and was unable to chew as a result.
• Philip II of Spain
• Charles V
• Maximilian I, Holy Roman Emperor
• Cymburgis of Masovia, Piast princess through whom the condition was brought into the Habsburg family