Introduction:Attention-deficit/hyperactivity disorder (ADHD) is defined as a stable pattern of attention deficits or impulsive hyperactivity that can interfere with the functioning, growth, and development of individuals. It is believed that both the type of asthma and the medications used to treat it exacerbate the symptoms of ADHD.Methods and Materials:The present study was a cross-sectional analytical study conducted to investigate the incidence of asthma in ADHD patients aged 4–12 years who were referred to Urmia University of Medical Sciences clinics and hospitals. In this study, ADHD patients were diagnosed through a psychiatric interview and based on a paediatric asthma questionnaire (approved by asthma and allergy organizations and scientific institutions), and individuals with suspected asthma were selected. All 101 ADHD patients referred to these clinics during the specified period were examined. Five patients were excluded from the study because of lack of cooperation or incomplete information. Then, the selected subjects were divided into two age groups of less than 5 years and between 5 and 12 years. The final diagnosis of asthma was made by clinical findings and demographic questionnaire in subjects younger than 5 years, while it was made by spirometry in subjects between 5 and 12 years. Data analysis was conducted using SPSS software.Results:The mean age of the 96 samples included in the study was 7.67 years with a standard deviation of 7.214. Sixteen of them (16.7%) were under 5 years of age and eighty of them (83.3%) were between 5 and 12 years of age. Asthma was diagnosed in 7 children under 5 years of age (7.3%) and in 14 children (14.6%) between 5 and 12 years of age. A total of 21 (21.9%) were diagnosed as having asthma after screening. On the basis of these results, the frequency of asthma according to classified age was significant (P=0.020). The frequency of asthma based on sex and birth rank was also examined, and none of these factors showed a significant association with asthma. Medications taken by the ADHD patients were also examined in this study. The most commonly used medications in both groups of patients with asthma and no asthmatic patients were a combination of risperidone and atomoxetine or risperidone alone. The prevalence of asthma in the target population was also assessed in terms of parental smoking.Conclusions:According to the results of this study, the incidence of asthma in ADHD patients aged 4–12 years is high, and this case is more frequent in subjects younger than 5 years than in subjects aged 5–12 years. It should be noted that according to the results of the present study, there was no significant association between birth rank, parental smoking, ADHD medication, and the frequency of asthma.