OBJECTIVES: According to the Asthma and Allergy Foundation of America, about 25.9 Million Americans have asthma and it has been increasing. Although children had higher prevalence of asthma compared with elderly people, the mortality rate is at it's highest for the patients aged 65 or older. There are many possible factors for asthma including smoking, air pollutions, and climate. However, quantitative observation is not enough especially for elderly people. We analyzed the relationship between the disease and climate. METHODS: The Medicare data and the data of National Centers for Environmental Information from 2010 to 2013 were employed. Patients with asthma were identified by ICD9 codes and we extracted the patients with asthma in Miami by county. The climate data in the region was obtained from WBAN. We analyzed the relationships between climate and asthma prevalence in each year. RESULTS:  Study population was 225,000 to 246,000 per year and asthma prevalence was about 1%.We analyzed associations of asthma prevalence and temperature difference in the day. The Pearson product-moment correlation coefficient was 0.52(p<0.01). We considered the two categories of days: (a) days which had higher daily temperature difference in comparison to the same ones in the previous year, (b) others. We compared the asthma prevalence in the two cases: 2011 versus 2012, 2012 versus 2013. We found that even if asthma prevalence was lower than the previous year, it appeared only within category (b), within category (a) there were no big differences. CONCLUSIONS:  We found an association between temperature difference in the day and asthma prevalence in elderly people. Although the annual asthma prevalence was decreased, it seemed to include influence of temperature difference (so-called risk factor). After adjustment for risk factor differences, asthma prevalence was not decreased from the original one. Accordingly, the risk factor and risk adjustment should be considered when conducting analysis of real world health care data.