The prognostic values of loss of heterozygosity (LOH) at loci frequently involved in non-small cell lung cancer and of KRAS2 gene mutations were studied in lung adenocarcinoma patients. LOHs were relatively common, ranging from 24% at chromosome 10p to 55% at chromosome 17p13. KRAS2 mutations at codon 12 were present in 26% of cases, were more common in male than in female patients and were associated with a smoking habit. No association between LOH at any site and clinical stage or survival rate was found. On the other hand, we observed a trend between the presence of any type of KRAS2 mutations and poor survival. Analysis of specific KRAS2 mutations showed a strong effect of Asp (GAT) and Val (GTT) mutations, resulting in a very poor survival compared with wild type group, whereas the most common mutation (Cys, TGT) was not associated with prognosis. Our results indicate the importance of specific activating mutations of the KRAS2 gene as genetic markers of clinical outcome for patients with lung adenocarcinoma.