A case of leiomyoma of the lung was described by our department 17 years ago. We now report three new cases of smooth muscle tumours of the lower respiratory tract: a leiomyoma of the lung, a leiomyosarcoma of the right main bronchus, and a leiomyoma of the trachea. Whereas in the previous case the tumour was bronchoscopically removed, all the recent tumours were surgically resected. All the patients have done well, including the one with the leiomyosarcoma who underwent surgery 7.5 years ago. One hundred and eighty cases of leiomyoma and leiomyosarcoma of the lung and trachea have been reported to date. Pulmonary leiomyoma most commonly presents as an asymptomatic solitary lung nodule. The endobronchial variety may cause cough, haemoptysis, or shortness of breath. Most of these tumours were dealt with by major pulmonary resection, although a lesser resection would have sufficed in many cases if a histological diagnosis had been established prior to surgery. Pulmonary leiomyosarcoma may occur at any age, and is much more common in females. The majority of the patients have thoracic symptoms. These neoplasms seem resistant to chemotherapy or radiotherapy and should be treated by radical resection whenever possible, which results in a 45% 5-year survival rate. Only seven cases of leiomyosarcoma and 12 cases of leiomyoma of the trachea have been reported. These usually cause respiratory obstruction and/or haemoptysis. The malignant as well as the benign tumour is probably best treated by complete surgical resection.