Abstract: This study evaluated 24 patients with lung cancer (CA) and 23 individuals with no smoking history or cancer in the family and without respiratory disease in childhood (CO). Peripheral blood lymphocytes was used to perform alkaline comet assay and to assess DNA damage as well as to evaluate methyl methane sulfonate (MMS) DNA repair after one hour and three hours at 37 ºC. The percentage of residual damage (RD) after three hours of MMS treatment, for each patient was assessed. The majority of patients were in the CA group, male patients, former smokers, with a history of smoking for 15 years and without associated comorbidities. Alkaline and residual damages were higher in the CA group when compared to controls (alkaline damage P = 0.015 and RD P = 0.05). After one hour of MMS treatment the DNA damage of the CA increased indicating failure to repair it, compared to the controls, and after three hours DNA repair was observed in both groups. Patients with lung cancer are mostly men, former smokers and with more than 15 years of tobacco consumption, undergoing chemotherapy, have high rates of DNA damage and deficiency in their ability to repair against induced damage when compared to controls.