This study reports the efficacy of adjuvant chemotherapy in stage IA non-small cell lung cancer (NSCLC) with vessel invasion (Vi). We sub-divided 322 patients with surgically resected pathological stage IA NSCLC into two groups according to Vi [non-Vi (n=237) and Vi (n=85)]. Both groups were compared with regard to age, gender, performance status, smoking habits, serum carcinoembryonic antigen level, extent of surgery, tumour size, histopathology, recurrence sites, and survival. The overall 5-year survival rates of non-Vi and Vi groups were 89.6% and 71.8% (P<0.001), respectively. Distant metastasis was observed more frequently in the Vi group (P<0.001, risk ratio: 9.06). Univariate and multivariable analyses identified poor performance status, squamous cell carcinoma, tumour size>or=15 mm and Vi as poor prognostic factors (P<0.05). The overall 5-year survival rate of stage IA Vi group nearly overlapped with that of patients with stage IB NSCLC. Retrospectively, oral uracil-tegafur chemotherapy increased the overall 5-year survival rate of stage IA Vi group by more than 25% (P=0.036). In conclusion, vessel invasion is a poor prognostic factor in patients with stage IA NSCLC. Prognosis of patients with Vi-stage IA NSCLC is similar to that of patients with stage IB NSCLC and is improved significantly by postoperative oral uracil-tegafur chemotherapy. Our preliminary study suggests that stage IA Vi group benefits from adjuvant chemotherapy.