We investigated the significance of cyclin D1 and cyclin E expression in resected tumors on the survival of patients with small adenocarcinomas of the lung. Seventy-two patients with resected tumors <2 cm in diameter and of pathological stage I were entered into the study. There were 29 males and 43 females, with a median age of 64 years (range 26-83 years). The patients underwent curative surgical resection for lung cancer between July 1992 and November 1999. The resected tumors were subjected to immunostaining for cyclin D1 and cyclin E expression. Twenty-six patients had tumors with >20% cyclin D1-positive cells, but only 1 patient had a tumor with >20% cyclin E-positive cells. When the survival of 72 patients was compared in relation to their oncogene expression, the overall survival of patients with positive expression of cyclin D1 was significantly worse than that of individuals whose tumors had negative expression of the gene (log-rank test p=0.0049). Increased expression of cyclin D1 but not of cyclin E is an indicator of poor prognosis in patients with small adenocarcinomas of the lung.