Adult onset Still's disease (AOSD) is a systemic inflammatory disease characterized primarily by a triad consisting of daily fever, arthritis and maculopapular exanthema. The pathogenesis and etiology of AOSD are unknown and the diagnosis, which can be very challenging, is often made by exclusion. Here, we report a case of a 61-year-old woman with a history of mild psoriatic arthritis, fever, arthritis and maculopapular exanthema. Her initial laboratory tests showed neutrophilic leukocytosis, hypertransaminasemia, and markedly elevated levels of the erythrocyte sedimentation rate and C-reactive protein. With a presumptive diagnosis of AOSD, based on Yamaguchi criteria, the patient started an extensive diagnostic work-up to exclude other potential differential diagnoses. With fluorodeoxyglucose (FDG) positron-emission tomography, a thyroid nodule with moderate FDG uptakes was detected. The fine needle aspiration biopsy led to diagnosis of papillary thyroid cancer. The history of psoriatic arthritis, the patient's age, and atypical features of the skin rash described as not concomitant with fever flares, suggested a diagnosis of paraneoplastic AOSD-like manifestations.