Three hundred and fourteen cases of peripheral lung tumours managed surgically over a 15-year period have been analysed to re-examine the effect of tumour size on the probability of survival up to five years after operation. The cases were classified into four groups according to the size of the primary. There was a significant inverse relationship between tumour size and five-year survival over the four groups (p less than 0.05) but this relationship did not hold for the largest tumours. The tumours over 6 cm did no worse than the group one size smaller (4.5-6.0 cm). Analysis of the survival in each group revealed a different pattern of annual loss in the largest tumours which suggested that this group included carcinomas self-selected for less metastatic potential. The peripheral tumours as a whole included more undifferentiated but fewer small cell carcinomas than the overall chest clinic figures. Within the peripheral tumours squamous carcinomas became more common and adenocarcinomas less common with increasing size. No small cell or adenocarcinomas were found among the five-year survivors in the large tumour group. Because 20% of patients with tumours over 6 cm lived for five years in this group of 314 patients we do not believe that they should be excluded from operative treatment on the basis of size alone.