Sweet's syndrome has a wide range of clinical manifestations. It may appear as a solitary cutaneous disorder but often it is associated with systemic signs and symptoms. This disorder might be idiopathic but it often is paraneoplastic or associated with medications or autoimmune diseases. In its systemic manifestation Sweet's disease resembles adult-onset Still's disease in many aspects. We present a case of a young man in whom Sweet's syndrome and Still's disease developed. Although the diagnosis of adult-onset Still's disease is made by exclusion, he fulfilled all the criteria of both conditions. Considering the clinical similarities of these diseases, it may be presumed that similar patients may have been overlooked in the past.