1. 124 cases were found out from 8047 persons who received the mass examination and the discovering rate was 1.5 per cent. 2. 140 cases were checked to be diabetics from 645 persons by their family trees examination with the discovering rate of 23 per cent. 3. Diabetics were found with the discovering rate of 25.6 per cent among persons whose mothers or fathers suffered from diabetes and with 21.13 per cent among persons whose parents had no diabetes. And the former per cent was higher a little than the latter. 4. The rate of having diabetes in their young age was higher among persons in so-called diabetes family trees than in the normal trees, and the death of some persons by the above diabetes of early age was noticed. 5. There were found 9 family trees which had cases more than 3 respectively and 4 family trees which had cases more than 4 being pointed out to be the deep and thick diabetes family trees. 6. It is very necessary to conduct the family trees investigation on the occasion of mass clinical examination. Its reason is as follows: We can find out new cases, especially the early age cases under 30 ages, and that, serious cases among rather small number of persons, and the persons, involving diabetics and non-diabetics, in the diabetes family trees should take care of their own meals from point of the so-called preventing medicine.