Summary. Epidemiological studies in psychiatry contribute to the knowledge of prevalence of mental disorders and rational planning of protection of mental health, and also enable the application of optional methods in primary, secondary and tertiary prevention. Based on the information provided by the Register of psychiatric activities of the Bjelovar General Hospital an epidemiological study of the hospital treated patients for the years 1980, 1985, 1990, 1995, and 1999 was made. In determining the diagnostic groups the authors used the International classification of diseases ICD10 and references of the WHO, adapting all the diagnostic entities to the valid classification. According to the Register, in the observed years of the twenty-year period, 4631 psychiatric patients, who make the sample of the study, were treated. The fall of the general number of psychiatric hospitalizations by 28.8%, the reduction of the proportion of men and women in the sample, and also the reduction of mortality were noted. In the observed period the fall of the general number of hospitalised alcoholics, and the increase of hospitalisations due to dementia, schizophrenia, affective disorders and critical conditions were visible. The differences in the results between the initial and the final year of the epidemiological study were analysed by the chi square test. Changing of the social system, the war and post-war occurrences have led to the series of changes in the epidemiological image of psychiatric hospitalisations. The results of the epidemiological study will help the evaluation, rational planning and further development in the protection of mental health of the inhabitants of Bjelovar region.