Sweet's syndrome is an acute febrile neutrophilic dermatosis marked by attacks of painful, plaque-forming inflammatory papules accompanied by fever, arthralgias, peripheral leukocytosis, a diffuse dermal neutrophilic infiltrate, and prompt resolution of symptoms and lesions with glucocorticoid therapy. There are many reports of drug-induced Sweet's syndrome to various medications including all- trans -retinoic acid, carbamazepine, hydralazine, levonorgestrel/ethinyl estradiol, minocycline, trimethoprim/sulfamethoxazole, and granulocyte colony-stimulating factor. We describe the first known case of Sweet's syndrome induced by pegfilgrastim, a pegylated form of granulocyte colony-stimulating factor with unique pharmacologic properties that may induce Sweet's syndrome in patients with no history of neutrophilic dermatoses associated with granulocyte colony-stimulating factor therapy.