Standard procedures for primary lymphoma of the sinonasal tract, before treatment and for therapeutic response evaluation include clinical examination, computed tomography and/or MRI. Many studies have demonstrated the utility of 18 FDG-PET for staging and for response assessment of lymphoma. We present here the cases of two patients, with primary lymphoma of the sinonasal tract, in which the 18 FDG PET evaluations showed positive images, suspecting the presence of residual lymphoma tissue. This hypothesis was refuted by a biopsy of the residual lesions. We believe that is important to have a figure showing the extent of inflammation as recommended by the reviewer. Unfortunately, as requested into the "Type of papers" we can use only one figure.We completed the References as recommended