BACKGROUND The objective of this study is to identify the most common aetiology of bronchiectasis in patients undergoing HRCT chest at Navi Mumbai. Further, to understand the demographical profile and anatomical distribution of bronchiectasis in these patients. MATERIALS AND METHODS This study included 30 patients within the age group of 10 -75 years who had all undergone an HRCT chest for a variety of chest symptoms such as breathlessness, cough, haemoptysis and fever with/without chills. These patients were scanned using a 64 slice Toshiba Aquilion CT machine. The scans were done in the supine position. For inspiratory scans, 1 mm thick sections were taken at 5 mm intervals from the lung apices to below the CP angles with 50 mAs, 120 kVp. Same parameters were used for the expiratory scans except in this the interval taken was 20 mm. RESULTS In this study, the male: female ratio was found to be 3: 2. The cause of bronchiectasis in most patients in this study was found to be post-infectious, Koch's being the commonest (66.67%) followed by Staphylococcus infection (13.33%), UIP (10%), fungal infection (6.67%) and COP (3.33%). The left lung was more commonly involved (56.67%) followed by the right lung (26.67%) and then bilateral involvement (16.67%). The upper lobes were most commonly involved (43.3%) followed by the lower lobes (36.6%). Middle lobe involvement was 20%. Other associated findings included tree in bud appearance in 10 cases, air space consolidation in 6 cases, mucous plugs in 3 cases, pleural effusion and cavity in 2 cases each. CONCLUSION It is important to perform HRCT in symptomatic cases of suspected bronchiectasis. HRCT is a very sensitive modality for showing bronchiectasis which is characterised by the lack of bronchial tapering, bronchi visible in the peripheral 1 cm of the lungs and an increased broncho-arterial ratio producing the 'signet-ring sign.' Bronchiectasis is caused by a complex cycle of repeated inflammation and a defective immune response to suppress it. Haemoptysis is common and is usually a sequelae of tuberculosis. Commonly bronchiectasis results from necrotising bacterial infections, but in this study Koch's infection evolved as the most common cause of bronchiectasis.