A relationship between idiopathic spontaneous pneumothorax (ISP) and visible parenchymal bullae and blebs has been reported. The causal relationship between blebs and bullae and ISP is questionable. Consequently, resection of the involved area is only indicated if it predisposes to recurrence of the pneumothorax. CT studies on 101 cases of ISP were analysed. The presence of bullae and their distribution was then related to the first and recurrent pneumothorax. CT demonstrated bullae in 56% of first ISP and in 64% of recurrent ISP, mostly among older patients. Only eight patients had bullae larger than 2 cm on the side of the pneumothorax. The location of the bullae was not a factor in predicting recurrent pneumothorax.