The impact of sickle cell anaemia (SCA) on respiratory function of children must be determined if their management is to be optimised. Pulmonary diffusing capacity (DL(CO)), corrected for haemoglobin (DL(COc)), therefore was assessed in 24 children with SCA and 24 ethnic matched controls, mean age 11 (range 7-16) years. To determine if any differences found correlated with other measures of lung function, spirometry was undertaken and lung volumes assessed. The SCA children compared to the controls had lower weight (p=0.01), body mass index (p=0.002), DL(CO) (p<0.0001), K(CO) (p=0.003), V(CSB) (p=0.01), FEV(1) (p<0.0001) and FVC (p<0.0001), but greater K(COc) (p=0.001). K(COc) results correlated significantly with PEF (r=-0.58, p=0.02), but not TLC(pleth) (p=0.36), FEV(1) (0.39) or FVC (p=0.36). In conclusion, when corrected for haemoglobin levels, the SCA children compared to controls of similar age had elevated gas transfer per unit lung volume results. Our results suggest this abnormality is independent of other lung function abnormalities.