The effectiveness of simple aspiration of pneumothorax with an intravenous cannula was evaluated in 34 patients who would otherwise have been treated by intercostal tube drainage with underwater seal. The procedure was successful in 25 patients (73.5%). The following features were associated with a successful outcome: (a) age below 50 years, (b) absence of underlying lung disease, (c) pneumothorax size not exceeding 50%, (d) volume of air aspirated less than 3000 ml, and (e) no previous pneumothorax. There were no complications encountered. Successfully treated patients benefitted from a shorter hospitalisation stay. The potential use of this procedure in treating selected patients in an outpatient setting should be explored.