Behçet's disease (BD) is a chronic, multi-systemic vasculitis of every size and type vessels. It was first described by Hulusi Behçet, a Turkish Professor of Dermatology, in 1937, as a triad of recurrent aphthous stomatitis, genital aphthae, and relapsing uveitis. [1] The prevalence of BD is highest in the countries of the Eastern Mediterranean, Middle East, and Eastern Asian rim. [2] Familial Mediterranean fever (FMF) is an autoinflammatory disorder characterized by periodic fever and serosal inflammation. [3] It is common in the Turkish, Armenian, Arabic, and Sephardic Jewish populations. [4] The Mediterranean Fever (MEFV) gene, associated with FMF, is located on chromosome 16 and encodes a 781-amino-acid protein termed pyrin. [5] Behçet's disease and FMF share a number of features in common in terms of clinical features and geographic distribution. Several studies have suggested that MEFV mutations may be associated with BD. [1,6-9] Herein, we report a case of coexistence of FMF and BD, and to discuss the immunopathogenetic mechanisms for possible associations among these two autoinflammatory diseases. CASE REPORT A 19-year-old female with a 10-year history of BD was referred to our outpatient rheumatology clinic with bilateral ankle joint arthritis, abdominal pain, and fever. The patient presented with a history of two years of recurrent attacks for fever, abdominal pain, and arthralgia for about four days. She was admitted to our emergency room with these complaints two days ago. She was followed for 24 hours, and no other pathology which could explain abdominal pain and infection findings for fever were able to be found. Therefore, she was referred to our outpatient rheumatology clinic. In the records of emergency room, fever was 39 °C, and laboratory ABSTRACT Behçet's disease (BD) is a chronic, multi-systemic vasculitis, characterized by a triad of recurrent aphthous stomatitis, genital aphthae, and uveitis. It is common in the Eastern Mediterranean, Middle East, and Eastern Asian countries. Familial Mediterranean fever (FMF) is an autosomal recessive autoinflammatory disorder, which is common seen in the Turkish, Armenian, Arabic, and Sephardic Jewish populations. It is characterized by recurrent episodes of fever, peritonitis, pleuritis, arthritis, and erysipelas-like skin lesions. Behçet's disease and FMF have common clinical features and geographic distribution. Herein, we present a 19-year-old female patient with coexistence of FMF and BD in the light of literature data.