Smoking causes significant morbidity and mortality worldwide, mainly in developed countries. In addition, it is the cause of numerous diseases in the body, despite the fact that the prevalence of tobacco use is decreasing. Nursing students, as future professionals, should be aware of action plans for cessation and information designed for smokers. To determine the level of knowledge among nursing students about smoking-related diseases and analyze the prevalence of student who smoke at the University of Leon, Spain, a descriptive cross-sectional study was carried out in which students were given an anonymous questionnaire, which was previously validated, during the 2021–2022 academic year. In a sample of 477 (79.5%) nursing students, a smoking prevalence of 17.6% was obtained. In addition, students’ knowledge about the diseases directly caused by tobacco consumption and others associated with exposure to environmental smoke was assessed, and in both cases (8.03 points of 9 for consumption and 5.24 of 6 to exposure), scores were obtained that allow us to state that students do not know for sure the types of diseases that are related to tobacco use and passive smoking. In spite of this, it is necessary to continue to reduce the prevalence of smoking through different programs implemented in schools and universities, as it is also necessary to improve teaching plans when explaining smoking-related diseases, so that students, in the future, will be able to advise patients correctly.