This paper reviews the historical aspects of expatriate mental health, and comments on the paucity of literature in the medical and psychiatric journals. Data obtained from 397 expatriate probands examined during overseas service are described. It was noted that there was a high incidence of affective and adjustment disorders. The results showed six areas significantly related to those with affective disorders at interview, namely a history of consultation for psychological problems in out-patient departments or with the patient's own doctor, a history of depressed mood, and a family history of suicide, psychosis or personality disorder. Subjects with adjustment disorders at interview showed a significant positive correlation with four stressors (occupational anxiety, home country anxieties, acculturation and physical ill-health), but showed a negative association with a past personal history of consultation for psychological problems at out-patient departments or with their own doctors. These findings are discussed and practical applications suggested for improving expatriate mental health.