To assess whether an accurate diagnosis of pneumothorax can be made on a single chest film, 233 pairs of inspiratory (I) and expiratory (E) chest films taken in an accident and emergency (A&E) department for suspected pneumothorax were reviewed by two A&E officers and three radiologists. The films were assessed for the presence of pneumothorax by viewing the I film in isolation and, after an interval, by viewing the paired I and E films together. Fifty-four of the patients had a pneumothorax. The five observers missed 23 pneumothoraces (8.5% of total) on the I film alone which were correctly diagnosed on the paired I and E films, the three radiologists missed 10/162 pneumothoraces on the I film alone which were correctly identified on the I and E films (6%) and the two A&E officers 13/108 (12.5%). The use of a single inspiratory chest film for suspected pneumothorax could result in pneumothoraces being missed, particularly by less experienced observers and therefore we believe that paired I and E films should continue to be used routinely for suspected pneumothorax.