Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal malignancy of the gastrointestinal tract. PET/CT is a common diagnostic tool and is also used for therapy monitoring. GISTs typically show strong (18)F-fluorodeoxyglucose (FDG) uptake. Here we present two cases of GIST with unusually low/negative FDG uptake. FDG negativity does not preclude the diagnosis of a GIST.