The effects of heat and cold waves have been studied as risk factors for cardiovascular and respiratory diseases. However, few studies have examined the effect of diurnal temperature changes on health. We hypothesized that the diurnal temperature range (DTR) may affect the rate of hospital admissions for cardiovascular- and respiratory-related diseases, and therefore investigated the risk of hospital admissions of cardiovascular (stroke, myocardial infarction, ischemic heart disease, cardiac failure, cardiac disease, and arrhythmia) and respiratory (asthma, chronic obstructive pulmonary disease, and pneumonia) diseases attributable to DTR in four metropolitan areas in Korea during 2003-2006. The area-combined effects of DTR on some cardiovascular and respiratory diseases were significantly increased by an increment of DTR. In particular, the effects on cardiac failure and asthma were significant with the percentage change of hospital admissions per 1 °C increment of DTR at 3.0% (95% CI, 1.4-4.6) and 1.1% (95% CI, 0.1-2.0), respectively, among 9 diseases. For those 75. years and older, the DTR effect on asthma admissions was greater than in those aged under 75. years. These results support the hypothesis of a positive association between DTR and cardiovascular and respiratory hospital admission. © 2012 Elsevier B.V.