Even in the same atmospheric environment, various living conditions would cause different human mortality. Diseases and deaths occur much in the same ways under similar livelihood circumstances. With this in view, the authoresses have long been studying what bearings climate as part of the human environment will bring about upon health, diseases, deaths, etc. In this paper, they intend to summarize their findings about the seasonal variation of mortality from cerebrovascular diseases and to reconsider its medico-geographical and its biometeorological aspects.<br> Epidemiologists have revealed that cerebrovascular ailments are often caused by daily diet as well as by hereditary high blood pressure. Clinical physicians have found that “cold in winter” acts as a trigger for the occurrence of these senile maladies, parti-cularly in the case of the old-aged liable to high blood pressure and cerebrovascular dis-order. But there is much room left for further study on the direct relations between the occurrence of and mortality from cerebrovascular diseases, on the one hand, and, on the other, climate, temperature and other meteorological conditions, especially the re-gional and chronological differences, if any, in these relations in connection with the progress of dietary life, drugs and medical care.<br> The authoresses study begins with the seasonal variation of deaths from cerebrovas-cular diseases and the chronological and regional differences in the pattern of such variation from the viewpoint of medical geography and biometeorology.<br> Based upon vital statistics in the 1950's, two types of the seasonal variation of cerebrovascular deaths are distinguished 1) A marked winter concentration of mortality is found in the intermediate latitudes, comparatively warm countries, such as Japan., England and Italy, and 2) the seasonal variation is rather moderate in the North Eu-ropean countries in the highh latitude zone and North America where severe cold pre-vails in the north.<br> Then, a chronological comparison is made in the relationship between the seasonal variation of temperature and of mortality from cerebrovascular diseases in England, the City of New York and Tokyo (the central 23 wards, excluding the suburban areas) for which vital statistics are available since 1900. The following facts are thus found<br> 1) In Tokyo, deaths from cerebrovascular diseases curve up considerably in sum-mer in the 1900's. While two maxima in summer and winter are apparent from the 1920's through the 1930's, a single peak of winter becomes dominant in the 1950's, the peak getting higher and higher in recent years. Such chronological changes in cere-brovascular deaths can generally be said to hold true in the whole country.<br> 2) In England, the winter peak alone does appear earlier in the 1920's, and such concentration in the cold months is becoming all the more conspicuous in the past years.<br>3) Strikingly contrasted to such spectacular changes decade by decade, New York has experienced only little change in the seasonal variation of cerebrovascular mortality since the 1930's. The seasonal variation for New York proves to be the smallest in the American city.<br> Generally speaking, the seasonal variation of cerebrovascular mortality is moderate in cold regions where man cannot live without fully equipped heating facilities, while on the other hand such deaths increase conspicuously in winter in comparatively warm zones. In New York, be it emphasized, the central heating system was widely adopted already in the 1930's, if not so perfectly as at present. The above geographical differ-ences in the pattern of seasonal variation come from none other than the different methods of room heating in the cold season.