The ubiquitin-proteasome system controls the activity and stability of a variety of cellular proteins that affect cellular homeostasis through the regulation of signaling cascades. The activity of this system is associated with the occurrence and progression of squamous cell carcinoma of the oral cavity, since the specific proteolysis of most intracellular proteins involved in the pathogenesis of cancer occurs with the help this system. The original article presents the parameters of the ubiquitin-proteasome system in leukoplakia and squamous cell carcinoma of the oral cavity, and proposes a model for assessing the risk of potentially malignant disease malignancy.