Sweet's syndrome was described in 1964 by Robert Douglas Sweet, as an entity he named acute febrile neutrophilic dermatosis. It is characterized by five main features: 1) sudden appearance of erythematous and tender plaques on the face, neck and extremities; 2) fever; 3) polymorphonuclear leukocytes; 4) predominantly neutrophilic dense infiltrate in the dermis, and 5) rapid response to steroid therapy. Sweet's syndrome can be classified into five groups: idiopathic, parainflammatory, paraneoplastic, drug-induced, and pregnancy-related. Twenty percent of cases are associated with malignancies; 85% out of them involve hematologic alignancies and the remaining 15%, solid tumors. A series of seven cases of Sweet's syndrome associated with neoplasms which were diagnosed from 2002 to 2006 is presented. Six cases were related to oncohematologic diseases and one to solid tumors. These results highlight the importance of the diagnosis of the syndrome, since it may predict tumor relapse or underlying disease progression. The timely use of diagnostic and treatment methods may improve the quality of life of these patients. The fact that oncology patients take multiple medications (a colony-stimulating factor) which may be associated with the onset of this entity must also be considered in excluding possible causes. Keywords: Prognosis; Skin Neoplasms; Sweet's syndrome