A retrospective immunohistological analysis of 100 patients with pT1-3 N0 and pT1-3 N1 gastric adenocarcinoma demonstrated a high frequency of micro-involvement in the removed lymph nodes. The presence of three or more tumour cells in more than 10 per cent of the lymph nodes was of significant prognostic value in the pN0 cases. Multivariate analysis identified micro-involvement as an independent prognostic factor. The results explain why patients benefit from lymphadenectomy even if the removed lymph nodes are not involved by tumour (pN0) in routine histological examination. The frequent occurrence of micro-involvement is a strong argument favouring routine D2 lymph node dissection in gastric cancer surgery in patients with lymph node metastasis.