Asthma –COPD overlap is characterized by persistent airflow limitation with several features usually associated with COPD. It is identified in clinical practice by the features it shares with both asthma and COPD. A stepwise approach to diagnosis is advised, with recognition of the presence of chronic airway disease, syndromic categorization as characteristic asthma, characteristic COPD or ACO, confirmation of chronic airflow limitation by spirometry and, if necessary, referral for specialized investigations. The aim of the study was to determine the prevalence and to study various clinical characteristics of the patients with ACO. METHODS: This was a prospective observational study in 79 patients with chronic airflow obstruction. The patients were categorized as asthma, COPD or ACO as per the GINA guidelines. Prevalence of ACO, various clinical characteristics, genetic, environmental factors and comorbidities associated with ACO were analysed.