Background & Objective: Congenital melanocytic nevi are benign proliferation of melanocyte in the epidermis and dermis in fetal period. These nevi are mostly benign but there is a risk of malignancy in case of firmness, discharge, pain and bleeding. Aim of this study was to describe if they enlarge, these congenital nevi and risk factors of malignancy in this group of patients.

 Methods: This study was a descriptive analytic cross sectional study. The cases were the people who referred to Sina Hospital Dermatology Clinic of Tabriz and had congenital melancytic nevi, the number of cases was 54 for all of them filled out questionnaires aires and the findings were investigated with SPSS and T- test.

 Results: In 50% of the patients, nevi were smaller than 1.5^cm and 3.7% over 20^cm and 46.3% between 1.5 -20^cm. Secondary changes were found in 38% of cases in which the commonest one was hair growth. Other secondary changes were growth, site, Dermal keratosis, Hyper pigmentation and skin infection. About appearance of nevi border of them were regular and smooth in 92.6% and irregular in 7.4%. Suspicious sign of Malignancy findings were considered in 5.6% of cases and in 1.9% of cases developed malignant melanoma.

 Conclusion: This study showed that most of our nevi were benign and the risk of malignancy was low. But presence of induration and rapid growth in moderate or giant congenital melanocytic nevi should trigger us to evaluate malignancy of them. Furthermore malignancy risk in small nevi were much lower than the larger one.