The clinical efficacy of photodynamic therapy (PDT) was evaluated in cases of early-stage lung cancer. Haematoporphyrin derivative was used as a photosensitizer and an argon dye laser and excimer dye laser were used as the light sources. A total of 199 lesions in 165 patients with lung cancer were treated by PDT. Forty-five lesions in 40 patients, which had been detected only by sputum cytology, were endoscopically suggestive of early-stage lung cancer. All patients showed normal chest X-ray findings. Thirty lesions in 26 patients were treated by PDT only, with or without other conservative treatment because of poor pulmonary function or for other reasons. All lesions initially showed complete remission. Recurrences were seen in three cases. Nine patients died of unrelated causes and one patient died after a recurrence. The other 16 patients are alive and apparently free of the disease. Fifteen lesions were treated surgically after PDT because the effectiveness of PDT was uncertain. Among these, five lesions showed complete remission histologically. Three of the PDT-only patients have now survived for more than five years. The longest surviving patient has gone eight years without apparent recurrence.