Abstract Introduction. Adult Onset Still Disease (AOSD) is a systemic inflammatory disease, of unknown etiology, affecting young adults. It is, at least in part, a diagnosis of exclusion. Characterized by high fever with spikes, with or without complete defervescence outside of said spikes, arthritis, and evanescent rash. Also, sore throat, hepatomegaly, splenomegaly, serositis, lymphadenopathy might be present. Fatal risk is mainly attributed to Macrophage Activation Syndrome. Biologically its main trait is a marked inflammatory syndrome with unusually elevated ferritin levels. Case presentation. 31 year old male, known with a history of alopecia areata, treated with Diprophos, last dose one month prior to admission, with fever, odynophagia, sore throat, diffuse myalgia, debuted twelve days before. On blood samples, at admission and during his hospital stay, marked inflammatory signs are present (elevated ESR up to 100mm/h, C-reactive protein up to 37.4mg/dl and marked ferritin of 6240 ng/ml) accompanied by leukocytosis with neutrophilia, lymphopenia, low grade normochromic, normocytic anemia, thrombocytosis, slightly elevated liver function tests, cholestasis (GGT 502 U/L, ALKP 255 U/L) with normal bilirubin, D-dimers over 3000 with lowering values to 1344, spontaneous INR at 1.57. Normal values for rheumatoid factor, no antinuclear antibodies present, negative serology for hepatitis B, C, HIV, atypical bacterial infections (Chlamydia, Coxiella, Mycoplasma) Epstein-Barr Virus, syphilis, vasculitis markers (pANCA, cANCA) and anti-double stranded DNA, all coupled with 5 different hemocultures and 3 different urocultures all negative. Repeated ENT evaluation was within normal, chest X-Ray, echocardiography and CT scans of neck, thorax and abdomen reported back no significant abnormalities. Thus, by applying Yamaguchi criteria, after a complex evaluation of the case, the diagnosis is AOSD, and during his stay at the Internal Medicine department of Col ea Clinical Hospital, despite antiinflammatory, antithermic, antibiotic and corticosteroid treatment, the patient remains symptomatic, with high fever (up to 38.8 degrees Celsius) with chills and diffuse myalgias. At the indication of a rheumatologist, inside a specialty clinic, pulse-therapy with Methylprednisolone is initiated (500mgs a day for 5 days) with fever remission for more than 72 hours. The corticosteroid treatment is continued at home, with the patient self-monitoring for symptoms. Two months after corticoid therapy was initiated, the patient is almost without any symptoms (alopecia areata still present partially) and the inflammatory syndrome is greatly diminished. Conclusion. We present the case of a 31 year old male, with AOSD, defined by Yamaguchi criteria, with persistent symptomatology, mainly as high fever, without response to usual treatment, with the exception of pulse-therapy with Methylprednisolone. The diagnosis proved to be difficult, in part being one of exclusion, but also the clinical presentation, so unspecific, might easily lead to a different diagnosis.