The relation between tumor-associated macrophage (TAM) density and the density of microvessels was investigated in specimens from 113 patients with pulmonary adenocarcinoma, as was the influence of TAM density on prognosis. The rank correlation test revealed a significant relation between TAM density and microvessel density (y = 14.418 + 0.863x, r = 0.454, p > 0.0001). A significant difference in patient survival rate was detected between tumors with a TAM density defined as high and those with a TAM density defined as low (p < 0.01). Multivariate analysis also showed that TAM density was significantly related to survival (p < 0.05). These data indicate that TAM infiltration may contribute to tumor angiogenesis, and that TAM density is a useful prognostic marker in pulmonary adenocarcinoma.