Pigmentation of the oral mucosa is a common finding in clinical practice, which includes numerous conditions and lesions that lead to a change in the color of the tissue. They are etiologically and morphologically different, resulting from deposition of endogenous and exogenous pigments and can be blue, brown or black. Exogenous pigmentation of the oral mucosa usually occurs through action of amalgam, graphite, tobacco smoke products, drugs, and chromogenic bacteria. The most common pigmentation of the mucous membrane is the amalgam tattoo created by accidental implantation of amalgam into the soft tissue. The endogenous pigmentation of the oral mucosa is most often explained by the presence of pigments from the organism such as hemoglobin, hemosiderin and melanin. Pigmentation etiologically caused by endogenous pigments include melanotic macula, nevocellular and blue nevus, as well as malignant melanoma. Many systemic diseases can cause pigmentation of the mucous membrane. Oral malignant melanoma occurs very rarely, but its appearance is very dangerous. As a consequence of trauma, ecchymoses and petechiae may develop, as erythrocyte extravasation occurs in the submucosa, resulting in red-colored macula. Vascular lesions can also be noticed on the mucous membrane of the oral cavity, in which case diascopy is used to confirm them. Pigmentation diagnosis is not an easy task to perform, but the frequency and localization of lesions facilitate the diagnostics. Definitive diagnosis most commonly involves biopsy and taking a pathohistological sample in order to distinguish between clinically similar lesions.