Background: Pulmonary dysfunction has been reported in patients with β-thalassaemia major but data are conflicting and the association with iron overload remains unclear. Objectives: To determine the pattern of pulmonary dysfunction in patients with β-thalassaemia major and their associations with iron overload. Methods: Subjects with β-thalassaemia major were recruited for lung function assessment. Serum ferritin and magnetic resonance imaging (MRI) measurements of iron status of the myocardium and the liver were used as surrogate indexes of body iron content. A subgroup of this cohort provided data on the longitudinal progress of their lung function. Results: One hundred and one patients were recruited with a mean age of 25.1 years (SD 7.9 years). Thirty-eight (38%) and five (5%) had restrictive and obstructive lung function deficits, respectively. There was a significant correlation between MRI myocardial T2* relaxation time and forced vital capacity (r=0.291, p=0.048). Higher MRI cardiac T2* relaxation time was associated with lower risk of having restrictive lung function deficit (Odds ratio (OR): 0.94; 95% CI: 0.89-0.99; p=0.023) after adjusting for age, gender and BMI. Twenty-three subjects underwent lung function reassessment with a mean follow-up duration of 13 years. Overall, they did not demonstrate significant changes in pulmonary function over time, 3 patients who had normal lung function at baseline developed restrictive abnormality at follow-up. Conclusions: Restrictive lung disease is prevalent in patients with β-thalassaemia major, and the severity correlates with myocardial iron overload. Monitoring of lung function in this group of patients is important, particularly for those with iron overload.