Gaucher disease is caused by a deficiency of glucocerebrosidase, resulting in hepatosplenomegaly, pancytopenia, growth retardation and skeletal involvement. We analyzed data on genotype and key clinical parameters in 35 Japanese patients with Gaucher disease type 1. Our data demonstrated that over 60% of patients had onset of Gaucher disease signs/symptoms at less than 5 years. Sixty percent and 46% of evaluable patients were splenectomized and developed severe bone involvement, respectively. Within mean follow-up periods of 8 years and 4 months, mean relative height and weight, severity score index and platelet count all worsened to a highly significant degree. These data suggest that type 1 Gaucher disease tends to be severe and progressive in Japanese patients, most of whom would be suitable for treatment and might indeed require earlier and more aggressive therapy.