A rare systemic inflammatory disease with characteristics of early onset granulomatous arthritis, uveitis and skin rash. Blau syndrome (BS) now refers to both the familial and sporadic (formerly early-onset sarcoidosis) form of the same disease. Skin rash is usually the first manifestation, joint manifestations usually begin before the age of 10 with painless cyst-like swellings on the back of feet and wrists. Camptodactyly due to hypertrophic tenosynovitis is often described as the disease progresses. The spectrum of clinical manifestations includes fever, malignant systemic and pulmonary hypertension, granulomatous large-vessel vasculitis and granulomatous inflammation of the liver, kidneys and lung. BS is due to an inherited or de novo mutation in the NOD2 gene (16q12), responsible for alterations in the innate immune response, inflammation and cell death. BS is an autosomal dominant disorder in the familial form.