Background This Cochrane review was first published in 2005 and updated in 2007, 2012 and now 2015. Acute bronchiolitis is the leading cause of medical emergencies during winter in children younger than two years of age. Chest physiotherapy is sometimes used to assist infants in the clearance of secretions in order to decrease ventilatory effort. Objectives To determine the efficacy of chest physiotherapy in infants aged less than 24 months old with acute bronchiolitis. A secondary objective was to determine the efficacy of different techniques of chest physiotherapy (for example, vibration and percussion and passive forced exhalation). Search methods We searched CENTRAL (2015, Issue 9) (accessed 8 July 2015), MEDLINE (1966 to July 2015), MEDLINE in-process and other non-indexed citations (July 2015), EMBASE (1990 to July 2015), CINAHL (1982 to July 2015), LILACS (1985 to July 2015), Web of Science (1985 to July 2015) and Pedro (1929 to July 2015). Selection criteria Randomised controlled trials (RCTs) in which chest physiotherapy was compared against no intervention or against another type of physiotherapy in bronchiolitis patients younger than 24 months of age. Data collection and analysis Two review authors independently extracted data. Primary outcomes were change in the severity status of bronchiolitis and time to recovery. Secondary outcomes were respiratory parameters, duration of oxygen supplementation, length of hospital stay, use of bronchodilators and steroids, adverse events and parents’ impression of physiotherapy benefit. No pooling of data was possible.