A neuropsychiatric assessment is no more or less than a good psychiatric assessment, comprising a psychiatric and medical history. Electrodiagnostic techniques have an important role in neuropsychiatric diagnosis. Magneto-encephalography (MEG) measures the small magnetic fields generated by neuronal currents and may be regarded as the magnetic counterpart of the electroencephalograms (EEG). Neuroimaging techniques can be broadly divided into structural and functional. The two major techniques of structural imaging are computed tomography (CT) and magnetic resonance imaging (MRI). Functional imaging techniques are used primarily to provide information on metabolism, blood flow, neurochemistry or activity of the brain. Mental disorder is characterised by the presence of mental symptoms that are judged to be the direct physiological consequence of a general medical condition. The essential features are prominent hallucinations or delusions that are judged to be due to the direct physiological effects of the medical condition or substance.