The aim of the study was to characterize patients at risk for exacerbations of their asthma as a result of the Tottori-Ken Seibu earthquake and to identify factors that predict exacerbation of asthma after an earthquake. A retrospective cohort study-analysis was conducted of 156 asthmatic patients, aged 18 to 89 years, who were out-patients of Tottori University Hospital and who had completely recorded their asthmatic symptoms and measured their peak expiratory flow (PEF) rates for more than one year prior to the earthquake. Seventeen (11%) patients who experienced the earthquake were identified as having an exacerbation within one month after the earthquake. Diurnal variability of PEF during the month after the earthquake was compared to values during a matched month one year previously. When factors associated with exacerbation were identified by a review of the medical case notes and the contribution of these factors to the exacerbation was determined using multivariate analysis, airflow limitation was shown to be independently associated with exacerbation after the earthquake. Acute asthma attacks are more likely to occur within the first week after the earthquake event without diurnal PEF variability. Asthma is likely to worsen after an earthquake.