This case report describes Blau syndrome in monozygotic twins. The disease ran an identical course in both patients, starting with a maculopapulous exanthema at one year of age. Skin biopsies showed epithelioid cell granulomas with multinucleated giant cells. Shortly after arthritis and periarticular swelling developed and uveitis appeared at 8 years of age. Treatment consisted of prednisolone and methotrexate, and from 18 years of age of infliximab, with good effect. DNA analysis showed de novo R334W mutation in the CARD15 gene. The patients have now been followed for 19 years and are in good clinical condition.