The purpose of this study was to elucidate the asthma knowledge level of primary school teachers in Istanbul, and factors associated with this subject. Seven hundred and ninety-two teachers from 73 randomly selected primary schools in Istanbul were included in this study. Although Istanbul primary school teachers generally have a satisfactory knowledge on asthma, they lack knowledge on triggers of asthma attacks and on the management of the disease. The knowledge level of the teachers was related to gender but was not related to age, education level, length of tenure, location of primary school and county. We think that an asthma education program is needed for Turkish teachers to increase their understanding about what asthma is, its impact and how to meet the needs of a child with asthma to achieve improved wellbeing and school attendance.