In the evaluation and management of bronchial asthma, simple instruments for measurements of the peak expiratory flow (PEF) rate are needed. The aim of this study was to determine normal PEF values of Turkish children living in Istanbul. This is the largest study conducted in Turkey. In a cross-sectional study, we measured PEF in 2791 healthy schoolchildren (1468 boys and 1323 girls) aged 7-14 years, with a Mini Wright peak flow meter. We entered height, age, and sex into the regression equation. The equation for prediction of PEF in boys was calculated as (3.5 X height [cm]) + (9.2 X age [years]) - 256.5, (p < 0.0001; r = 0.83) and for girls as (3.3 X height [cm]) + (10.2 X age [years]) - 263.7 (p < 0.0001; r = 0.81). We found that PEF values of Turkish children were similar to British and Danish children, but significant differences were noted with Greek, Irish, Mexican American, African-American, and white American children. Our results were significantly lower compared with another study conducted in Adana, a small southern city (<1 million inhabitants) in Turkey. Istanbul being a cosmopolitan big city (>7 millions inhabitants) can reflect more reliably real PEF values of Turkish children. We concluded that our findings would serve as an important basis for preparing centile curves for normal PEF values for Turkish children.