Acute exacerbation of asthma can induce respiratory alkalosis, which not only decreases serum level of ionized calcium but also results in cerebral vasoconstriction. Several studies have cleared that respiratory alkalosis and decreased CO2-pressure in blood (hypocapnia) can increase neuronal excitability and its epileptogenic activity. This situation may also increase CNS dopamine level and risk of convulsion, therefore we planned this study to assess the association of asthma and epilepsy. In a cross-sectional and analytical study, 800 asthmatic children, who were referred to Specialists` Clinic of Tabriz University of Medical Sciences (TUMS) from January 2004-2008 underwent surveillance for epilepsy; then resultant data analyzed by Z-test for a ratio. About 26/800 children found to be affected simultaneously by asthma and epilepsy, including 15 males and 11 females whose age average was 6±2.1 years (95% CI = 3.5-6.7). The prevalence of epilepsy in asthmatic patients was higher than general population and this difference was statistically meaningful (p<0.05). According to prevalence of epilepsy, which is about 1% in general population and 3.25% in our asthmatic patients and because of possible hypocapnia and resultant respiratory alkalosis during asthma exacerbations, the probability of recurrent convulsive attacks in those, who have simultaneous asthma and epilepsy will be much higher and needs special care and treatment.