[18F]-Fluorodeoxy-d-glucose (FDG) positron emission tomography–computed tomography (PET-CT) is known to be highly accurate in differentiating benign lesions from malignant lesions. In rare cases, benign tumours, viral infections and sarcoidosis of the skin have been reported to show FDG uptake, but the mechanism remains unclear. Here we report the first documented case of seborrhoeic keratosis (SK) showing increased FDG uptake. FDG PET-CT can be used to detect enhanced glycolysis of tumour cells by measuring increased levels of glucose transporters (GLUTs) indicative of higher glucose uptake. GLUT1 and GLUT3 expression in this case was compared with that in PET-negative SK and two normal skin samples using quantitative polymerase chain reaction with paraffin-embedded tissue. The expression of GLUT1 and GLUT3 was higher in PET-positive SK than in PET-negative SK or normal skin. More specifically, the expression of GLUT3 was observed only in the PET-positive case. This study revealed that high GLUT1 and GLUT3 expression in SK might be associated with the uptake of FDG.