Blau syndrome is familial, juvenile, systemic granulomatosis with primary clinical findings of uveitis, arthritis, and dermatitis. Although rare, Blau syndrome shares aspects of the more common diseases sarcoidosis and Crohn's disease. The clinical findings of Blau syndrome are similar to those of juvenile sarcoidosis and mutations of Blau syndrome are on the same chromosome 16 gene that confers susceptibility to Crohn's disease, CARD15. The product of this gene is a component of the innate immune system involved in bacterial pathogen surveillance. Mycobacterium avium subsp. paratuberculosis (MAP) has been implicated as a causative agent of sarcoidosis and Crohn's disease. The presence of MAP in Blau syndrome tissue was postulated and archival tissues of individuals with Blau syndrome were acquired to test for the DNA of MAP. Six tissues of five patients representing three kindred were tested. The tissues were granulomatous lesions of skin, synovium, liver and kidney. Paratuberculosis was detected in all tissues. Its presence in these multi-system disease tissues expands the argument for the disease-causing role of MAP beyond the gut and positions MAP for consideration as a “superantigen”.