We have reported that thymidine phosphorylase (dThdPase) is identical to platelet derived-endothelial cell growth factor and that it has an angiogenic activity in vitro and in human carcinoma tissues as well as gastric carcinoma. Recently, we revealed that dThdPase may have an another function(s) besides angiogenesis in vitro and in human solid tumors. Using immunohistochemistry, we examined retrospectively whether the expression of dThdPase was correlated with tumor growth, comparing it with the proliferating cell nuclear antigen labeling index (PCNA LI) and examining their prognostic significance in 116 patients with gastric carcinoma. A direct correlation of these two factors was observed (R=0.659, P<0.001). A multivariate Cox regression analysis showed that both dThdPase positivity and PCNA LI were independent prognostic factors, as were depth of invasion and lymph node metastasis. Furthermore, the patients with dThdPase-positive/high PCNA LI tumors had the worst prognoses. The combination of dThdPase and PCNA expression is a better tool for predicting the prognosis of patients with gastric carcinoma than the expression of either of them alone. These results raise the possibility that dThdPase may have a function(s) involved in tumor growth besides angiogenesis.