During oncological treatments, body mass index (BMI) and weight loss (WL) are important prognostic factors, but can be influenced by nutrition therapy. The aim of the study was to collect data on BMI and WL of patients with lung cancer and on the nutritional therapy influencing malnutrition. In our multicenter, retrospective study involving 1616 patients, data were collected using a questionnaire with 51 questions, and statistical analysis was performed with descriptive, and multivariate analysis methods with IBM SPSS 20 software. According to the method of Martin, based on BMI and WL, patients were ranked on a scale of 0 to 4 (grade 0 24.9%; grade 1 20.7%; grade 2 14.9%; grade 3 22.4%; grade 4 17.0%). Based on this data low BMI and WL may affect survival in 75.1%. In contrast, only 37.6% of patients received nutritional therapy, based on 47 different strategies. The data substituted into the prognostic matrix highlights that weight loss may shorten patients' survival. The 47 strategies indicate that the use of nutritional therapy is inconsistent throughout this patient cohort.