A 34-year-old male patient who had left orchiectomy and received three cycles of chemotherapy for testicular mix germ cell carcinoma was referred for [.sup.18]fluorine-fluorodeoxyglucose ([.sup.18]F-FDG) positron emission tomography/computed tomography (PET/CT) for complaints of weight loss and fever. PET/CT showed multiple and progressive [.sup.18]F-FDG uptakes in supra and infra diaphragmatic lymphatic regions, and multiple abnormal [.sup.18]F-FDG uptakes were noted in the lytic formed skeletal lesions. Clinicians remain in doubt regarding the multiple metastatic lesions without elevated serum tumor marker levels (alpha-fetoprotein, beta-human chorionic gonadotrophin, CA19-9, and carcinoembryonic antigen). Biopsy of the lytic lesion in the iliac bone revealed granulomatous inflammation suggestive of sarcoidosis. Systemic prednisone at 20-40 mg/daily was started. [.sup.18]F-FDG PET/CT images showed complete metabolic response to prednisone 8 months following the start of treatment. Keywords: Systemic sarcoidosis, testis carcinoma, [.sup.18]F-FDG PET/CT Orsiektomi yapilan ve testis mikst germ hucreli karsinomu tanisi nedeni ile 3 kur kemoterapi alan 34 yasindaki erkek hastada, kilo kaybi sikayeti nedeniyle nuks hastalik suphesi ile [.sup.18]flor-florodeoksiglukoz ([.sup.18]F-FDG) pozitron emisyon tomografi/bilgisayarli tomografi (PET/BT) goruntulemesi yapildi. PET/BT'de supra ve infra diyafragmatik lenfatik istasyonlarda cok sayida ve patolojik FDG tutulumu gozlendi. Ayrica litik gorunumlu cok sayida iskelet lezyonlarinda da anormal [.sup.18]F-FDG tutulumu kaydedildi. Klinisyen, serum tumor belirtec (alfa feto protein, beta insan koryonik gonadotropin, CA19-9 ve karsinoembriyonik antijen) duzeyi yukselmemis metastatik multipl lezyonlar konusunda suphelenerek olguya iliak kemikteki litik lezyondan biyopsi incelemesi onerdi. Histopatolojik sonuc sarkoidoz dusunduren granulomatoz inflamasyon gosteren odak olarak raporlanmasi uzerine gunluk 2040 mg/gun sistemik prednizon baslandi. Sistemik prednizon tedavisine baslandiktan 8 ay sonraki [.sup.18]F-FDG PET/BT goruntuleri tam metabolik yanit gostermektedir. Anahtar kelimeler: Sistemik sarkoidoz, testis karsinomu, [.sup.18]F-FDG PET/BT