BACKGROUND Oral lichen planus (OLP) and oral lichenoid lesions (OLL) are considered potentially malignant disorders with a cancer incidence of around 1% of cases, although this estimation is controversial. The aim of this study was to analyze the cancer incidence in a case series of patients with OLP and OLL and to explore clinicopathological aspects that may cause underestimation of the cancer incidence in these diseases. METHODS A retrospective study was conducted of 102 patients diagnosed with OLP (n = 21, 20.58%) or OLL (n = 81) between January 2006 and January 2016. Patients were informed of the risk of malignization and followed up annually. The number of sessions programmed for each patient was compared with the number actually attended. Follow-up was classified as complete (100% attendance), good (75-99%), moderate (25-74%), or poor (<25% attendance) compliance. RESULTS Cancer was developed by four patients (3.9%), three males and one male. One of these developed three carcinomas, which were diagnosed at the follow-up visit (two in lower gingiva, one in floor of mouth); one had OLL and the other three had OLP. The carcinoma developed in mucosal areas with no OLP or OLL involvement in three of these patients, while OLP and cancer were diagnosed simultaneously in the fourth. Of the six carcinomas diagnosed, five (83.3%) were T1 and one (16.7%) T2. None were N+, and all patients remain alive and disease-free. CONCLUSIONS The cancer incidence in OLP and OLL appears to be underestimated due to the strict exclusion criteria usually imposed.