Different studies have shown that carrying an alpha-1 antitrypsin (AAT) deficiency allele is an independent risk factor for developing lung cancer (LC). However, to date, little is known regarding whether carrying a deficiency allele may be a prognostic factor in the evolution of LC. A prospective observational study was carried out which consecutively included patients diagnosed with LC in University Hospital "Nuestra Señora de Candelaria" between December 2017 and August 2020. A blood sample was taken from each of the patients in order to determine both AAT serum concentration and genotype. Based on AAT genotype, patients were divided into the deficiency (Pi*≠MM) or non-deficiency (Pi*=MM) group. One hundred and sixty-four patients were included. The average length of follow-up was 13±10 months. Patients were classified as stage I (4.2%), stage II (8.3%), stage III (31.2%) and stage IV (56.3%), according to tumour, node and metastasis (TNM) staging. Twenty-eight patients (17%) were carriers of a deficiency allele (6 Pi*MS, 1 Pi*MZ, 1 Pi*MMheerlen). No significant differences were found with respect to baseline characteristics between Pi*≠MM and Pi*=MM. Patients in the Pi*≠MM group had a higher risk of death in the first 6 months after the LC diagnosis compared to Pi*=MM subjects (HR =2.04; 95% CI: 1.04-4.0; P=0.038). The presence of an AAT deficiency genotype could be a potential prognostic marker in LC. However, larger studies that justify these findings are needed.