Moles, the medical term being Nevi, vary in color from yellow-brown to black. They may be small or large; flat or raised; smooth, hairy, or verrucous; and have a broad or pedunculated base. Moles may rarely undergo malignant change and become malignant melanomas. They may be separated into groups according to their propensity to become malignant; in many instances, clinical and histologic appearances can be correlated. Though this classification is practical, it is not invariably reliable. About 25% of malignant melanomas do not develop from a preceding mole. Intradermal nevi (common moles), in which the malanocytes are found in the corium - not in the epidermis - are benign. Hairy mores are usually intradermal and are not precursors of melanomas. Junctional nevi may be flat or raised; the melanocytes are found at the junction of the dermis and epidermis. Though more susceptible to activation, only a small percentage become malignant. Active functional nevi contain some changed cells characteristic of early or premalignant lesions. Melanomas not infrequently develop from this type of nevus. Clinical evidence which reflects possible malignant changes includes increased size or pigmentation of moles. Childhood nevi are usually flat and initially of the junctional type, becoming intradermal subsequently. Histologic examination may show changes characteristic of benign juvenile melanoma, but malignant melanoma is rare before puberty. The decision to remove a pigmented nevus need not be made until the child reaches age 9 or 10. Pigmented nevi are commonly confused with freckles. Excision by a specialist of all malignant or suspected lesions is indicated. Histologic examination is mandatory. Many nevi are removed for purely cosmetic reasons and in these cases excision need not be wide. Excision is recommended when a pigmented nevus shows increasing pigmentation, redistribution of color or a halo of pigment around the base, or when any nevus increases in size, bleeds, ulcerates or crusts. In general, malignant melanomas develop more readily from moles on the lower legs and on the mucous membranes than from lesions located elsewhere. It frequently has been emphasized that pigmented moles subjected to constant irritation or trauma show a relatively high incidence of malignant changes, and should be removed. Clinical judgment is to be exercised.