Diagnosis and prevention of lysosomal storage diseases (LSD) in the former Soviet Union (FSU) is based on the interaction of various local counselling units with the Department of Inherited Metabolic Diseases (DIMD) at the Research Center of Medical Genetics (RAMS). Work began in 1982 using standard, as well as newly developed biochemical techniques. 25 different LSD were diagnosed in 445 patients from 404 families. 106 pregnancies in families at risk were monitored prenatally, and 25 affected fetuses were diagnosed and aborted. The clinical spectrum of diagnosed lysosomal storage diseases (LSD) was surprisingly heterogeneous. Besides classical forms of LSD numerous atypical forms were discovered. They included juvenile and adult forms of some sphingolipidoses manifesting as progressive dystonia, spinocerebellar degeneration and hebephrenic schizophrenia, as well as an atypical form of mucolipidosis III in which the clinical phenotype bore an obvious resemblance to that of mucopolysaccharidosis (MPS) VI. The incidence of MPS was much higher than that of other LSD. It was evaluated as 1:15000 for two regions of the FSU. This investigation revealed some peculiarities of the ethnic distribution of MPS in populations of the FSU and supported the high prevalence of the gene for Tay-Sachs disease gene in Ashkenazi Jews.