OBJECTIVE One important step in tumour invasion is the penetration of the basement membrane. Matrix metalloproteinases (MMPs) play a key role in the migration of normal and malignant cells through the basement membrane. The aim of this study was to investigate correlations between matrix metalloproteinase 2 (MMP-2) immunoreactivity and currently used classification systems and possible relationships between lymph node metastasis and MMP-2 expression. RESULTS This prospective study analysed specimens obtained from 114 gastric cancer patients (mean age 64 years; range 33-86 years) who underwent gastrectomy with extended lymphadenectomy. All specimens were categorized according to UICC classification, WHO classification, tumour differentiation, Laurén classification, Ming classification and Goseki classification. Formalin-fixed paraffin-embedded tumour specimens were stained using an avidin-biotin complex peroxidase assay. MMP-2 expression in the tumour epithelium was studied by immunohistochemistry with semiquantitative (score 0-3) evaluation. The MMP-2 staining pattern was positive (score 1-3) in 93 (81.6%) specimens and negative (score 0) in 21 (18.4%) samples. No significant correlations were found between MMP-2 expression and other variables such as age, tumour differentiation, WHO, Lauren, Goseki, and Ming classifications. In contrast, the intensity of MMP-2 staining in tumour cells correlated significantly with depth of tumour infiltration (T-stage), lymph node metastasis (N-stage), distant metastasis (M-stage), and UICC stage. CONCLUSIONS Expression of MMP-2 is strongly associated with tumour progression and lymph node metastasis in gastric cancer. Therefore MMP-2 staining may be clinically useful as predictor of tumour progression, especially for lymph node metastasis.