Adult-onset Still disease (AOSD) is a rare systemic inflammatory disease, associated with characteristic clinical and laboratory findings, which, if interpreted incorrectly, may lead to errors in the diagnosis, delay treatment, and produce significant morbidity and mortality. We present a case illustrating how AOSD may masquerade as sepsis. Our patient is a 59-year-old woman admitted with high fever, severe arthralgias, myalgias, sore throat, evanescent maculopapular rash, leukocytosis, and elevated ferritin. On initial evaluation, sepsis was the first consideration; however, despite broad-spectrum antibiotics, the patient did not improve clinically. Finally, the diagnosis of AOSD was made based on Yamaguchi's criteria. Systemic corticosteroid treatment was started along with discontinuation of antibiotic therapy, with dramatic improvement after 3 days. Adult-onset Still disease can mimic sepsis and needs to be suspected if there is no response to antibiotics in the setting of an evanescent rash that tends to occur with fever. A discussion based on a review of the literature is presented.