Current classification of pulmonary adenocarcinoma includes noninvasive bronchioloalveolar carcinoma, mixed subtype adenocarcinoma, and several patterns of invasive carcinoma. The extent of invasion in mixed subtype adenocarcinoma is variable, and prior studies suggest that estimates of extent of desmoplasia or invasion and gross tumor size are predictors of survival. Pathologic review of 178 consecutive primary lung adenocarcinoma resections from 1997 to 2000 was performed blinded to outcome. Lymph node metastases were not present in adenocarcinomas with less then 0.6 cm of invasion. In multivariate analysis and in strata adjusted for stage, measurement of linear extent of invasion was significantly associated with survival whereas gross size measurement alone was not. Significant differences in median survival were observed when patients were divided into noninvasive, microinvasive (<0.6 cm invasion), and invasive subcategories. In conclusion, among lung adenocarcinomas, histologic assessment of invasive growth may provide valuable prognostic information, and tumors with invasion under 0.6 cm have a more indolent clinical course after resection.