Aims & Objectives: (1) To find out the prevalence of ADHD in urban primary school children (2)To find out the presence of any co-morbid disorders associated with ADHD. Settings and design: This is a cross sectional study of school children selected from 15 different Govt. Schools nearby Govt. Royapettah Hospital, attached to Govt. Kilpauk medical college, Chennai. Material & Methods: 1000 children aged between 5 and 11 years were randomly selected from 15 different schools in Chennai. The presence of ADHD was then assessed by using Vanderbilt assessment scale Teacher's version by their class teachers. Those children screened positive were verified and reassessed for the presence of any comorbid factors by using Child Behavioural Checklist (CBCL) scale. All children screened positive were subjected to psychiatrist evaluation. Results: The prevalence of ADHD among urban primary school children in Chennai, Tamilnadu was found to be 9.67%. Poor academic performance was the most common associated comorbid condition (18.75%), followed by poor social behaviour (17.7%). Conclusion: The present study shows Poor academic performance was the most common associated comorbid conditions, followed by poor social behaviour.