Granulomatous autoinflammatory diseases are monogenic syndromes caused by mutations in the region encoding for the nucleotide-binding domain region of the NOD2/CARD15 gene with subsequent dysregulation of the inflammatory response and formation of noncaseous granulomas. They include Blau syndrome (BS) and early-onset sarcoidosis (EOS); both are clinically and genetically indistinguishable between them and they are the familial (autosomal dominantly inherited) and sporadic forms of the same disease, respectively. We describe a case of EOS, misdiagnosed for 30 years such as "juvenile rheumatoid arthritis" before and "classic sarcoidosis" later. In our patient, we found a new de novo mutation (E383G) in NOD2 that has been reported only in a family of Japanese patients with BS. After long-term follow-up (42 months), infliximab maintained good efficacy and safety without any sign of disease relapse and side effects.