INTRODUCTION: In France, World War II lasted from 1939 to 1945. Under-nourishment was a national problem, and was more severe in mental hospitals. The mortality of psychiatric inpatients in France during World War II has long been a controversial issue in the country. LITERATURE FINDINGS: Some authors wrote of the "soft extermination" of 40 000 mental patients, although this has been proven false. The historical study published in 2007 by Isabelle von Bueltzingsloewen provides in-depth description and analysis of starvation due to food restrictions in French mental hospitals. Although the French official statistic services published detailed data, no demographic study has been published so far. Such studies have been conducted in Norway and in Finland. "The influence of a period of under-nourishment upon mortality in mental hospitals can rarely be seen with a clarity equal to that in this work. The strict rationing was the same for everybody, but, extra muros, there was private initiative and ingenuity to help in alleviating the distress. Naturally, patients in institution had no ability to act on their own. The immense increase during the period of war from 1941 to 1945 appeared both as an increase in the exact death-risk and as an increase in the disproportion with normal mortality. The men reacted more strongly than women; which is readily comprehensible on physiological grounds, as the rations were virtually the same for all." Excess mortality continued after the war. Even though under-nourishment had ceased, death rates from tuberculosis remained high the following year. Both papers state that the poor hygiene and bad living conditions existing in mental hospitals before the war worsened the effects of food restrictions. DEMOGRAPHIC DATA: French data were published by the General Statistics of France (SGF) that became the National Institute of Statistics and Economic Studies (Insee) in 1946. A series of datasets were published each year according to sex, diagnosis and type of psychiatric institution. In 1943, the outdated diagnostic classification was replaced by a more modern one, with reference to ICD. The same year, the age groups also changed (instead of 35-44, it became 30-39). Publication of data by type of institution was discontinued in 1943; from 1945 to 1948, the only available data concerned patients in hospital on 31st December, by age, sex and diagnosis. General population data were published by the National Institute of Demographic Studies (INED). The data referring to civilian population during the war are provided by the Human Mortality Database. This study covers number of people in hospital, mortality rates by sex, age, diagnosis and type of institution, and standardised mortality ratios. These refer to the civilian population which is more relevant since mental patients would not have been allowed to join the armed forces, even if they had not been in hospital. Finally, mortality trends in mental hospitals are compared with those in "hospices for old, disabled or incurable people", in order to ascertain whether all vulnerable populations in institutions suffered to the same extent. The results show that the number of inpatients in 1945 was about half the total recorded in 1940, due to fewer admissions and to a large increase in the number of deaths. However, the number of discharges increased in 1940, even though the number of admissions had begun to slow down: many patients were sent to places offering better food and hygiene. The number of deaths began to rise as from 1939. Mortality rates were high in 1940 and especially in 1941, when almost one man in three and more than one woman in five died. Global rates did not change in 1942. In December that year, a government order stated that mental patients should receive more food. Mortality rates went down in 1943 and 1944, but rates did not return to the prewar values until 1946. In 1939, mortality rates are high but only among patients of 70 years of age or more. In 1940, they were highest above 55; in 1941, rates between ages 15 and 54 were double those of the preceding year. Thus, even though excess mortality affected all ages, its strongest effects were felt from the older patients to the younger ones from 1939 to 1941. Trends according to diagnosis are difficult to interpret because of the change of classification in 1943. The patients suffered greatest hardship in public hospitals, which had no budget of their own and were run by the departments and lowest in private hospitals contributing to the public service, most of which were congregational and received religious funding. In 1941, standardised mortality ratios were more than three times higher than they were before the war. CONCLUSION: Comparison with people living in hospices shows that during the war mortality rates were 50% higher in these institutions, while they almost tripled in mental hospitals. The number of people who died of starvation and infectious diseases in mental hospitals from 1939 to 1945 can be estimated at about 45,500. However, mental patients were made specially vulnerable by circumstances that existed before the war in mental hospitals, in terms of food, hygiene and staffing, as suggested by an official document quoted in the paper.