Primary spontaneous pneumothorax (sudden collapse of the lung) occurs predominantly in young people; symptoms may include chest pain and breathlessness. The current recommended treatment is to re-expand the lung by inserting a tube through the chest wall, which can be painful and may result in complications. The patient remains in hospital until the lung re-expands and surgery is occasionally required to achieve this. However, simply observing the pneumothorax and allowing it to re-expand slowly may be as effective as inserting a tube. The objective of this study is to compare the current standard treatment using a tube, to simple observation. If simple observation is found to be effective and safe this new approach could result in major reductions in hospital admissions, reduced time off work for patients, fewer complications and lower overall costs to the public health system.