Objective: to determine the frequency of the different lesions of the oral mucosa in the clinical internship of the Faculty of Dentistry of the University of Costa Rica (UCR). Methodology: retrospective study of 263 reports of oral lesions recovered from the biopsies file of the Faculty of Dentistry of the UCR from 2008 to 2015. Information on sex, age, location of the lesion and histopathological diagnosis was collected and evaluated in a descriptive and qualitative manner. Results: cases of oral mucosal lesions affected women preferentially (n = 144, 54.8 %), the average age was 48.8 years (16.4 SD) and with lesions predominantly located in tongue (n = 68, 25.9%), gum (n = 62, 23.6 %) and lip (n = 61, 23.2 %). Non-neoplastic proliferative lesions (n ​​= 101, 38.7 %), potentially malignant lesions (n ​​= 29, 11.1%) and benign and malignant epithelial lesions (n ​​= 24, 9.1 %) were the most prevalent groups. The four most predominant lesions were fibrous hyperplasia, inflammatory fibrous hyperplasia, lichen planus and hyperkeratosis without atypia. Conclusions: non-neoplastic proliferative lesions were predominant, with the fibrous hyperplasia being the most prevalent lesion. These results may be useful to understand the distribution of oral diseases in a national sample.

Keywords: Biopsy, Oral pathology, Oral mucosa, Epidemiology, Costa Rica