SUMMARY
BACKGROUND: Congenital melanocytic nevi (CMN) are pigmented skin lesions usually present at birth. Rare varieties can develop and become clinically very large. Although they are benign nevomelanocytic neoplasms, all CMN may be precursors of the melanoma, regardless of their size. Individual risk of malignant transformation of melanocyte is determined by simultaneous action of exogenous and endogenous factors. The major exogenous risk factor is ultraviolet radiation. Leading roles among the endogenous factors are attributed to skin phenotype, gene mutation, sex hormones and their significance.CASE REPORT: We present a case of a 27 – year - old pregnant female patient with a congenital melanocytic nevus, which increased significantly in size, during her pregnancy. Estrogen levels increase during pregnancy and clinical evidence has suggested that melanocytes are estrogen - responsive. Nevi in a pregnant patient would exhibit increased expression of estrogen receptor ß (ERß) and thus enhanced the potential to respond to altered estrogen levels.CONCLUSION: All pigmented skin lesions should be carefully observed during pregnancy by a dermatologist due to the increased risk of malignant transformation, associated with the endocrine dependence. All lesions with visible changes should be removed surgically with appropriative anaesthesia.