Introduction Blau syndrome or early-onset sarcoidosis is a rare monogenic autoinflammatory granulomatous disease. It occurs with an autosomal dominant mutation in the nucleotide-binding oligomerization domain containing 2 gene, and the clinical manifestations typically appear in the first 20 years of life. Untreated disease can cause severe disability and blindness. Therefore, early and effective treatment is especially important to prevent eye and joint complications. This study aimed to show that tumor necrosis factor (TNF) inhibitors such as adalimumab are a good treatment option for patients with Blau syndrome or early-onset sarcoidosis. Case report We report the case of a patient with early-onset sarcoidosis who showed the clinical triad of dermatitis, arthritis, and uveitis. The patient had a history of atopic dermatitis-like skin disease at the age of 1 year. At the age of 2.5, she presented with arthritis in bilateral symmetrical wrist and knee joints and with gait disturbance. Bilateral vitritis was detected at the follow-up eye examination performed at the age of 3.5. Treatment was initiated with adalimumab, to which the patient had a very good response, particularly regarding the ocular symptoms. Conclusion Patients with Blau syndrome or early-onset sarcoidosis may be mistakenly diagnosed with juvenile idiopathic arthritis. Eye involvement may be more aggressive in this disease. Treatment with TNF-alpha inhibitors seems to be promising for Blau syndrome patients who do not have a satisfactory response to corticosteroids and conventional disease-modifying antirheumatic drugs.