Background: The blue nevus of the oral cavity is a rare lesion with important differential diagnoses. The plaque-type blue nevus is an uncommon variant of the blue nevus. Because of its particular clinical appearance, it can easily be confused with satellite metastases from malignant melanoma. The diagnosis usually requires a biopsy. Objectives: To describe the clinical and histological features of a plaque-type blue nevus of the buccal mucosa in a 20-year-old white woman, to review all intraoral blue nevi and all plaque-type blue nevi reported in the literature so far and to compare the criteria of blue nevi and nevus of Ota. Results: An intraoral blue nevus was described for the first time in 1959. Since then around 70 further cases have been documented. Our case is the first report of a plaque-type blue nevus of the oral cavity. Conclusions: The exceptional widespread intraoral blue nevus described herein can clinically be confused with an intraoral malignant melanoma, and it has a very similar clinical appearance as the intraoral part of nevus of Ota. Apart from the clinical resemblance, there is also some degree of histological overlap of the dermal melanocytoses. Transitional states between blue nevus and nevus of Ota may occur clinically and histologically.