Background: Reference values of peak expiratory flow (PEF) in Indian adults have to date been derived locally, using an old (Wright) scale peak flow meter. There are thus no reliable reference values for PEF for Indians and this formed the aim of the study. Materials and Methods: A European Union (EU) scale peak flow meter (PFM) was used for the study. A respiratory health and demographic questionnaire was administered to 1000 male and female adults from randomly selected locations in the country in this multi centric study. The locations represented different geographic, ethnic, and socioeconomic backgrounds. Patients were stratified according to height and age. The PEF values were measured using the Breathometer™ (Cipla Ltd., India) with EU scale. Reference equations were derived from multiple regression analysis. Results: A total of 3608 participants were excluded. In 80% of the remaining 6138 healthy adults (M: 3720; F: 2418), the predicted regression equations were derived. Gender, age, and height were the significant determinants of PEF. The equations in L/minute are: Females: PEF = -1.454 (Age) + 2.368 (Height) Males: PEF = -1.807 (Age) + 3.206 (Height). The derived equation was validated by comparing the predicted PEF values with the measured values in the remaining sample of 20% (Mean ΔPEF: M = 1.85 L/minute, CI = -2.76, 6.47; F = 1.64, CI = -2.89, 6.18). An Indian adult with average height and age was found to have approximately 30% lower PEF compared to the corresponding European adult using the Nunn and Gregg equation. Conclusion: We derived reference values of PEF for Indian adults using a validated EU scale peak flow meter
