AIMS: To determine if there is any correlation between vascular invasion and prognosis in non-small cell carcinoma of the lung; and to look specifically at invasion of vascular channels by tumour cells. METHODS: Eighty seven patients undergoing lobectomy or pneumonectomy for adenocarcinoma or squamous carcinoma were followed up for five years. The histological sections were studied for evidence of vascular invasion using an elastic van Gieson stain. The incidence of intimal fibrosis in arteries and veins was noted and the proportion with vascular invasion evaluated using a scoring system. The presence or absence of lymphatic permeation and tumour necrosis were noted. Survival data were analysed using the log rank test. RESULTS: The overall five year survival was 32%. There were 64 squamous cell carcinomas and 23 adenocarcinomas. Vascular invasion was seen in 77% of patients and lymphatic invasion in 44%. Neither the presence nor absence nor the proportion of blood vessels showing vascular invasion showed any relation to prognosis. Intimal fibrosis and tumour necrosis were unrelated to prognosis. Patients with lymphatic permeation had recurrence and died earlier than those without. CONCLUSION: The presence of arterial or venous invasion by adenocarcinoma or squamous carcinoma of the lung was unrelated to survival; lymphatic permeation was associated with poor prognosis. The two common non-small cell lung cancers behaved differently from other solid tumours, where vascular invasion was a significant factor in determination of prognosis. The presence of intimal fibrosis was unrelated to prognosis.