Abstract Background:Diabetes mellitus is a leading cause of morbidity and mortality among children across the world and is responsible for a growing proportion of global healthcare expenditure. However, limited data are available on lung dysfunction in children with diabetes. Aim:The aim of this study was to evaluate the pulmonary function changes in children with type 1 diabetes mellitus (T1DM). Methods:We studied 60 children with T1DM (mean age 10.5 ± 2.32 years; disease duration 2.45 ± 0.6 years, and 50 healthy control children (mean age 9.9 ± 2.5 years). Spirometry was performed for all individuals to measure forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1/FVC ratio, and peak expiratory flow rate (PEFR). Glycemic control was assessed on the basis of glycated hemoglobin (HbA1c), with HbA1c values 8% considered to indicate good glycemic control, and HbA1c values ⩾8% to indicate poor control. Results:There was significant reduction in all spirometeric parameters in diabetic children in comparison with healthy control children. Children with poor glycemic control had significant impairment in lung functions compared with those with good glycemic control. Conclusions:T1DM in children leads to impairment of lung functions and this impairment increases with poor glycemic control.