Background. A 48 year-old woman presented with an 18month history of bizarre and complex delusions on a background of social, behavioral and cognitive decline over several years. Her psychosis progressed despite receiving high doses of antipsychotics. The patient's father also had a psychotic episode in his 40s. He subsequently developed motor neuron disease, which caused his death at 68 years of age.Investigations. Physical examination, neuropsychological testing, nerve conduction studies, brain MRI and transcranial magnetic stimulation.Diagnosis. On the basis of the patient's age at onset of the delusions, imaging findings and family history, a diagnosis of frontotemporal dementia (FTD) was favored over a primary psychotic disorder. The ubiquitin-positive and TAR DNA binding protein 43-positive inclusions that were found at autopsy confirmed the diagnosis of FTD.Management. The patient was treated with various antipsychotics at high doses; however, her delusions continued to progress. No disease-specific treatments for FTD currently exist.