The relative height at the onset of insulin-dependent diabetes mellitus was recorded in 340 cases from Japan and 191 cases from Pittsburgh, U.S.A. In Pittsburgh, the children diagnosed after puberty were shorter than normal whereas those diagnosed prior to puberty were much taller than normal. However, in Japan, there was no association between age at onset and relative height; at every age the newly diabetic children had similar relative heights to the non-diabetic population. This discrepancy may be related to the 18-fold incidence difference between the two countries.