Brucellosis which is a endemic in Turkey, is a systemic infection which can affect any organ or system in the body. Since signs and symptoms of brucellosis resemble many other diseases, misdiagnosis and related increase in morbidity rate, are common. In this report, a case of brucellosis complicated with endocarditis, pyelonephritis, sacroileitis and thyroiditis, was presented. The case was a 32-years-old female patient in whom the diagnosis of brucellosis was delayed by 12 months since it was not taken into consideration during the clinical follow-up of the patient in various clinical centers. The patient was admitted to our center with the complaints of fever, headache, back pain, night sweats, fatigue, loss of appetite, weight loss, dysuria and polyuria. The patient had a history of consumption of raw milk and dairy products. Positive Brucella tube agglutination test (1/1280) and isolation of Brucella spp. in blood cultures led to the diagnosis of brucellosis. Sacroileitis was diagnosed upon pain on right hip joint movements, pain and restriction at the same joint in FABER test. The detection of vegetation during echocardiography, cardiac murmur during physical examination and the determination of increased ESR and CRP levels led to the diagnosis of endocarditis. Abdominal ultrasonography and urinalysis results (hematuria, proteinuria and pyuria) revealed pyelonephritis and increased free T3 and T4, decreased TSH and positive anti-thyroid autoantibodies (anti-TG, anti-TPO) revealed thyroiditis. Treatment was started with combination of rifampisin (1 x 600 mg/day) and doxycycline (2 x 100 mg/day). After the diagnosis of endocarditis, trimethoprim-sulfamethoxazole (3 x 960 mg/day) and streptomycin (1 x 1 g/day) were added to the treatment. Valve replacement surgery was planned, however, the patient didn't accept surgical intervention and antimicrobial treatment continued with streptomycin for 21 days and other antibiotics for six months. The patient exhibited significant improvement after the medical treatment. Although sacroileitis is a frequent complication of brucellosis, endocarditis, thyroiditis and pyelonephritis are among the rare complications. In cases of brucellosis with multiorgan involvement including endocarditis, successful results may be achieved by aggressive antimicrobial treatment. In endemic areas, brucellosis should always be taken into consideration in patients with fever of unknown origin and multisystem involvement.