Objective: To investigate the expression of paired like homeodomain 1 (PITX1) gene in lung adenocarcinoma and normal tissues and its correlation with clinicopathological features and prognosis. Methods: The GTX130779 and GSE85841 data sets in the Cancer Genome Atlas (TCGA) database and the Gene Expression Omnibus (GEO) were used to analyze the PITX1 gene in cancer tissues and adjacent tissues of lung adenocarcinoma patients. The expression level of PITX1 gene was verified in 40 patients with lung adenocarcinoma by real-time fluorescent quantitative PCR. COX regression was used to analyze the correlation between PITX1 gene and overall survival (OS) and recurrence-free survival (RFS) in patients with lung adenocarcinoma, and to analyze the correlation between the expression level and clinicopathological features of patients with lung adenocarcinoma. Results: Based on TCGA and GEO database analysis, PITX1 gene was highly expressed in lung adenocarcinoma tissues (P<0.01). The results of real-time quantitative PCR showed that the expression of PITX1 gene in lung adenocarcinoma tissues was significantly higher than that in normal adjacent tissues (P<0.001). The relative expression amounts of these two tissues were 1.064±0.077 and 0.641±0.044, respectively. Moreover, COX regression further analysis showed that the expression level of PITX1 gene was significantly correlated with TNM stage, lymph node metastasis status and tumor size in patients with lung adenocarcinoma (all P<0.05). At the same time, the up-regulation of PITX1 expression was significantly negatively correlated with OS and PFS in patients with lung adenocarcinoma. Conclusion: PITX1 gene is highly expressed in lung adenocarcinoma and is significantly associated with the prognosis of patients with lung adenocarcinoma.