BACKGROUND: Peak expiratory flow rate is a simple way of assessing severity of obstructive and hyper reactive airway diseases. Reference values may be used in assessment and management of asthma in children. It is also possible to predict values of PEFR, based on age, weight and height. OBJECTIVES: Determine factors affecting Peak expiratory flow rate. Derive Predictive normal values for Peak expiratory flow rate in School going children of Karaikal region. Derive Predictive equations correlating Peak expiratory flow Rate with age and anthropometric measurements METHODS: A School based, Cross-sectional study consisting of 700 school going children is undertaken to study the factors affecting the peak exploratory flow rate. Each child was examined clinically based on pre designed questionnaire. Anthropometric parameters like weight, height, chest circumference were measured. PEFR was recorded using Mini Wright's Peak flow meter. STATISTICAL ANALYSIS: Descriptive statistical analysis has been carried out in the present study[69,70]. Results on continuous measurements are presented on Mean +/- SD (Min-Max) and results on categorical measurements are presented in Number (%). Significance is assessed at 5 % level of significance. Analysis of variance and student t test has been used to find the significance of PEFR between age, gender and BMI. Pearson correlation has been used to find the significant relationship between PEFR and anthropometric parameters. Prediction equations by regression analysis is carried out. The Statistical software namely SPSS 15.0, Stata 8.0, MedCalc 9.0.1 and Systat 11.0 were used for the analysis of the data and Microsoft word and Excel have been used to generate graphs, tables etc. RESULTS AND CONCLUSIONS: Peak flow meter is an simple and cheap method of assessing the PEFR to assess children with chronic obstructive diseases, monitoring disease in asthma (prediction of exacerbation and monitoring therapeutic efficacy) Boys have marginally higher PEFR than girls. PEFR increases with age in boys and girls. PEFR has good correlation with weight, height, chest circumference and BMI. Predictive equations can be derived relating the PEFR with weight and height. PEFR values of children of Karaikal are lesser than those of other south Indian, north Indian and western children.