Introduction: International study on asthma was conducted to study the prevalence of Asthma symptoms among 13-14 year old children using written and video questionnaires during the early 90's. The aim of the present study (ISAAC) was to evaluate the agreement between the two questionnaires which were self-completed by the children. Methods: This study, which was a part of the third phase of International Study of Asthma and Allergy in Childhood (ISAAC) and performed exactly similar to phase1, was performed by National Research Institute of Tuberculosis and Lung Diseases (NRITLD) in two cities of Iran; Rasht and Tehran. All stages of the study were performed in accordance with ISAAC protocol. The present study discusses data related to children of Tehran. A total of 3100 school children aged 13-14 years were questioned about asthma symptoms using written and video questionnaires of ISAAC study. For statistical analysis, initially a descriptive study of the available data was performed. Thereafter, chance corrected agreement between the two questionnaires was evaluated using Cohen’s Kappa co-efficiency. Results: Of the total of 3100 children, 52.4% were male and 47.6% female, with a mean age of 13.6 years. Although the questions discussed in the two questionnaires were not exactly similar, the results of the video questionnaires showed a statistically significant lower positive response to asthma symptoms as compared to the written version. Kappa co-efficiency ranged between 0.06- 0.21 (mean=0.12), which is considered poor for all variables. Conclusion: Positive responses to having asthma symptoms were significantly higher using the written questionnaire compared to the video questionnaire. Similar to previous studies, agreement between the two was considered poor for all variables. Although factors such as language, culture, dwelling area, e.t.c. have special effects on results of these questionnaires, results indicate that the two questionnaires should be further studied and validated for this special group of patients in order to reach a better interpretation of prevalence of asthma symptoms.