A 24-year-old female presented with granulomatous slack skin (GSS) cutaneous T-cell lymphoma. The patient underwent systemic chemotherapy. Owing to the development of several chemotherapy-related complications, therapy was discontinued. Subsequently, disease progression was noted clinically. Our patient's disease progression was clearly demonstrated by 18F-fludeoxyglucose positron emission tomography (PET)/CT findings. PET/CT imaging findings of GSS have not yet previously been reported. In this report, we present PET/CT characteristics of a patient with GSS.