Sixty-six cases of multiple primary lung cancers were classified into 18 synchronous cancers and 48 metachronous cancers. They all occurred in tobacco-smoking men. The first group were symptomatic in 66 % of cases, the second were symptomatic in 40 % of cases. Six synchronous locations were unilateral and 12 were bilateral; 19 metachronous locations were ipsilateral and 29 were contralateral. Two cases had a third metachronous cancer. The resections of both tumours were performed in 11 out of 18 cases of synchronous cancers and 15 out of 48 cases of metachronous cancers. There were 2 deaths related to metachronous cancers. No patient with synchronous cancers survived 5 years after resection. One third of patients survived 5 years after resection of a metachronous cancer. Synchronous cancers represent an advanced stage. Metachronous cancers are diagnosed too late.