This study reports the psychiatric morbidity in 116 patients with definite multiple sclerosis (MS). The presence of brain pathology was investigated using magnetic resonance imaging (MRI). A group of 48 physically disabled controls suffering from rheumatic or neurological conditions not involving the brain was used for comparison. Normative MRI data were obtained from a group of 40 healthy volunteers. Psychiatric morbidity was significantly higher in the MS group with nearly half of the patients scoring as cases at interview. There was no evidence to suggest that psychiatric symptoms in isolation were the first manifestation of MS in the present material. The presence of psychiatric illness at interview was significantly related to the degree of social stress as perceived by the patient. The severity of MRI abnormalities was greater in those with longer histories and greater physical disability, but did not show a significant relationship with global measures of psychiatric disability. Of the various psychiatric symptoms elation was significantly correlated with the presence of widespread MRI abnormalities, while flattening of affect, delusions and thought disorder correlated with the degree of pathology in the temporo-parietal region.