Onset of obsessive-compulsive disorder (OCD) after the age of 50 years is rare, and should alert the physician to possible “organic” causes of OCD. These include infections, degenerative disorders, brain injury and cerebrovascular lesions, principally involving the frontal lobes and basal ganglia. The current patient had obsessive images, anxiety, auditory hallucinations and seizures following (possible) gliomatosis cerebri, with onset around 69 years of age. The atypical presentation, lesions involving the cortical-basal ganglia-thalamic-cortical circuit and the association with neurological signs/symptoms, was characteristic. However, late-onset OCD has not been commonly reported with diffuse lesions, and the association with gliomatosis cerebri is not known. This patient's case illustrates the need for careful screening of older patients with recently acquired OCD, and for further systematic study of OCD in the broad range of neuropsychiatric disorders affecting the elderly.