In the years 1970-1974 a total of 421 suicides were committed during treatment in 39 mental hospitals of the Netherlands. It is seen that the amount of suicides in the mental hospitals increased. The number of suicides was on an average 243.1 per 100.000 patients of 15 years and older a year. Compared with the ratel of suicide among the Dutch population those in the mental hospitals varied between 13 to 20 times higher in these years. 240 (= 57 per cent) of the patients were men and 181 (= 43 per cent) were women. 53 per cent of the patients were unmarried and 42 per cent were younger than 34 years. About a quarter of the patiens was schizophrenic, he psychotics seemings to be the most serious high-risk group. As regards the patient's stay in hospital 61 per cent had committed suicide during the first year of treatment, 24 per cent of the suicides had taken place during the first three months of treatment and 11 per cent after five years treatment. Concerning the legal state the most serious hig-risk group seemed to be unvoluntary admitted patients. 35 percent of the patients have been readmitted.