Background: Lung cancer is the leading cause of death among patients with cancer worldwide. The prevalence in Saudi Arabia is 4.1%, with an increasing trend in recent years. The increase in smoking in the population has been attributed to an increase in the incidence rate of lung cancer. Aim: To measure the prevalence of lung cancer among adult patients aged 18-54 in National Guard hospitals in Saudi Arabia. Methods and Material: Retrospective cohort study at National Guard hospitals in Saudi Arabia. The study included patients diagnosed with lung cancer between January 2016 and May 2021. The data collection sheet included the demographics (age and sex) and other information, such as diagnosis, type of lung cancer, smoking status, smoking type, and comorbidities. Results: This study included 140 participants. The sample comprised 59.3% men and 40.7% women. Seventy percent of the participants were between 43 and 54 years. Smokers constituted 45% of the sample, non-smokers 35.7%, while the remaining were of unknown status (19.3%); 26.4% were cigarette smokers, and 0.7% used water pipe smokers. A significant correlation was observed between the type of cancer and sex. Age was also associated with the smoking status. Conclusions: The number of cases of lung cancer is increasing, according to previous studies. Our data showed that most patients with lung cancer were male smokers aged >43 years. Screening programs for lung cancer can be used in this population. Screening should be encouraged in smokers of the appropriate age group for early detection of cancer and better outcomes.