Congenital melanocytic naevi (CMN) are present at birth, or very occasionally, arise in the first 2 years of life (tardive CMN). These lesions grow commensurate with the child, but tardive lesions can appear to grow more rapidly as the full extent of the CMN is often not initially apparent. The incidence ranges from 1 to 2% if all sizes are considered to approximately 1 in 20 000 for naevi projected to be greater than 20 cm in diameter in adulthood. 1 CMN are commonly classified according to maximum projected adult size and the total number of lesions at birth. The most recently proposed classification of size is small (CMN with an estimated diameter in adulthood of less than 1.5 cm), medium (M1, 1.5-10 cm and M2, 10-20 cm), large (L1, 20-30 cm, L2, 30-40 cm) and giant (G1, 40-60 cm, G2, >60 cm). 2 However, the authors prefer not to employ the term giant as it is often unacceptable to patients and families.The estimates of projected adult size are determined in a variety of ways, none of which are decidedly accurate, but remain the most reliable methods currently available. Some clinicians use a scaling factor applied to the CMN diameter at birth. More specifically, a CMN on the head is predicted to enlarge by a factor of 1.7, on the trunk and upper extremity by a factor of 2.8 and on the lower extremity by a factor of 3.3. 3 This approach is not without fault, as CMN often affect more than one region of the body and it does not account for significant differences in growth between the sexes. Other clinicians therefore estimate the projected adult size by drawing the child's CMN onto an adult body map, and estimating the longest non-circumferential diameter.CMN can present as isolated singular lesions or can be accompanied by a variable number of smaller discrete so-called satellite lesions. These lesions should be counted or estimated as each satellite lesion represents an additional CMN.