Emerging evidence suggests that microRNA, which are wellconserved, abundant and small regulatory RNA, may be involved in the pathogenesis of human cancers. We recently reported that expression of let-7 was frequently reduced in lung cancers, and that reduced let-7 expression was significantly associated with shorter patient survival. Two members of the double-stranded RNA-specific endonuclease family, Dicer and Drosha, convert precursor forms of microRNA into their mature forms using a stepwise process. In the present study, we examined expression levels of these genes in 67 non-small cell lung cancer cases, and found for the first time that Dicer expression levels were reduced in a fraction of lung cancers with a significant prognostic impact on the survival of surgically treated cases. It should be noted that multivariate COX regression analysis showed that the prognostic impact of Dicer (P = 0.001) appears to be independent of disease stage (P = 0.001), while logistic regression analysis demonstrated that the higher incidence of reduced Dicer expression in poorly differentiated tumors remained significant even after correction for other parameters (P = 0.02).