Air pollution is likely to have adverse effects on human health. This study was conducted to determine the effect of air pollution on respiratory disease hospital admission in Ahvaz, one of the most polluted cities in the Middle East. Daily information about respiratory disease admissions and air pollutants during 2008-2018 were inquired. Adjusted Quasi-Poisson regression combined with linear distributed lag models were used. There was a significant relation between increased O-3 and respiratory hospital admissions for 65-74 year olds, >= 75 year olds, and pyothorax-abscesses of the lung and mediastinum; between increased NO and respiratory hospital admissions for >= 75 year olds, chronic lower respiratory diseases, diseases of upper respiratory tract and respiratory diseases principally affecting the interstitium; between increased NO2 and respiratory hospital admissions for >= 75 year olds; between increased CO and respiratory hospital admissions and between increased SO2 and respiratory hospital admissions for >= 75 year olds. The risk of respiratory hospital admissions increased in both males and females for increase in PM2.5. Ambient O-3, NO, NO2 CO and SO2 can increase admission for respiratory diseases on the same day and at short lags in Ahvaz. This evidence emphasizes the need to implement policies for reducing air pollution. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.