Neurolymphomatosis (NL) is characterized by the infiltration of malignant lymphoma cells into peripheral nerves, nerve roots, plexuses, or cranial nerves. This is a very rare complication of mantle-cell lymphoma. Diagnosing NL is made difficult by cerebrospinal fluid cytology and bone-marrow biopsy results often being negative. NL can appear as the only sign of recurrence in a patient with a previous diagnosis of lymphoma. Here we present two cases of NL in patients with mantle-cell lymphoma diagnosed by positron emission tomography with deoxy-fluoro-D-glucose integrated with computed tomography.