Background Ethnic differences in lung function in school-aged children and adults are well recognized, but little is known about such differences in preschool children. We investigated whether differences exist in fraction of exhaled nitric oxide (F eno ), multiple-breath washout (MBW) indices, specific airways resistance (sRaw), and spirometry indices between healthy preschool children of South Asian and white European origin. Methods F eno , MBW indices (lung clearance index, functional residual capacity, conductive airways inhomogeneity, and acinar airways inhomogeneity), sRaw, and spirometry were measured in healthy South Asian and white children aged 4 to 6 years, and comparisons were made between the two groups. Statistical analyses were by multiple linear regression and t tests. Results Thirty-seven white (mean age 5.8 ± 0.7 years, 49% boys) and 31 South Asian children (mean age 5.4 ± 0.8 years, 52% boys) were recruited. F eno was, on average, 36% higher ( P < .05) in South Asian children compared with white children. FVC and FEV1 and fractions thereof (FEV0.75 and FEV0.5 ) z -scores were significantly lower in South Asian compared with white children by 0.69 ( P = .01), 0.76 ( P = .004), 0.76 ( P = .009), and 0.85 ( P = .002) z -scores, respectively, but there were no significant differences in FEV1 /FVC, FEF25-75 , sRaw, or MBW indices. Conclusions Differences in F eno and forced expiratory lung volumes between South Asian and white children exist from a very young age. Ethnic differences should be taken into account when interpreting lung function results in preschool children for effective management of respiratory conditions.