Directly age standardized rates of first admission schizophrenia in Denmark (1991: 5.1 million inhabitants) decreased significantly with a slope of -0.16 and -0.13/100,000 inhabitants fifteen years and above for males and females respectively from 1971 to 1991 when examined by help of the Danish nation-wide psychiatric case register in the Institute of Psychiatric Demography, Aarhus. A control for changes in diagnostic delay/changing diagnostic patterns does not affect the findings. Various nosological factors might cause the decrease, e.g. changing structure in organization of treatment facilities, decreasing number of beds (50% in Denmark during the period investigated) and correlated with this: increasing suicide rates among pretreatment schizophrenics, increasing rates of schizophrenics not yet diagnosed in shelters for homeless and in institutions for criminals. The decrease might be genuine. In connection with this the theories about damage to the fetus during the gestation period are briefly discussed.