Since Kraepelin delineated dementia praecox as a disease entity constr
uct, epidemiological studies conducted since the beginning of the cent
ury have produced remarkably consistent estimates of its prevalence, i
ncidence and lifetime risk across various populations and geographic a
reas. A similar pattern emerged from the WHO ten-country study on firs
t-contact incidence of schizophrenia. The diagnostic concept of dement
ia praecox originally used by Kraepelin and that of schizophrenia empl
oyed in the WHO studies were found to overlap extensively, indicating
continuity over time. However, the findings of a similar incidence of
schizophrenia in diverse populations and across time periods are unusu
al for a multifactorial disease and are compatible with at least two a
lternative interpretations that have different implications for the se
arch for genetic and environmental causes of the disorder. (C) 1997 El
sevier Science B.V.