Antoni Gaudí i Cornet, Catalan architect and one of the most important visual artists of the 19th and 20th centuries, suffered from a recurrent and often persistent arthritis since he was 6 years old. His diagnosis is uncertain but juvenile idiopathic arthritis is most likely. He coped successfully with his rheumatic illness during his life. It is proposed that his arthritis may have influenced him to the development of 2 of his major skills: observation power and analysis of nature.