The aim of the present study was to investigate the association between blood groups and life expectancy. We compared frequencies of ABO blood group in 269 centenarians (persons over 100 years) living in Tokyo and those in regionally matched controls (n=7153). Frequencies of blood types A, O, B, and AB in centenarians were 34.2, 28.3, 29.4, and 8.2%, respectively, while those in controls were 38.6, 30.1, 21.9, and 9.4%, respectively. Blood type B was observed more frequently in centenarians than in controls (chi(2)=8.41, P=0.04). This tendency also was true in comparison between centenarians and 118 elderly old individuals of the 7153. Approximate one-third of the centenarians were free from serious diseases such as malignancy. However, blood types were not associated with such medical records. Our findings suggest that blood type B might be associated with exceptional longevity. Responsible mechanisms need to be investigated.