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Abstract:  Linear and whorled nevoid hypermelanosis is a sporadic pigmentary anomaly occurring within the first weeks of life, characterized clinically by swirls and streaks of macular hyperpigmentation following the lines of Blaschko. Histologically it shows only epidermal melanosis. Underlying chromosomal mosaicism has been demonstrated in only a few published cases. Progressive cribriform and zosteriform hyperpigmentation is considered to be the localized variant of linear and whorled nevoid hypermelanosis. We report a retrospective study on 16 children referred consecutively over a 10-year period for evaluation of segmental, linear or swirled hyperpigmentation distributed along the lines of Blashko, consistent with a diagnosis of linear and whorled nevoid hypermelanosis. Associated abnormalities were found only in one out of six patients with the diffuse form (linear and whorled nevoid hypermelanosis-type) and in none of the remaining 10 children presenting the unilateral form (progressive cribriform and zosteriform hyperpigmentation-type). A long-term follow-up did not disclose further abnormalities. The authors discuss the nosologic position of this entity with respect to hypomelanosis of Ito. Linear and whorled nevoid hypermelanosis and hypomelanosis of Ito should be not considered single entities, but be rather grouped as a heterogeneous collection of nonspecific pigmentary disorders caused by genetic mosaicism. Skin findings in these diseases can differ according to the pigmentation in the normal cell line and whether the second line contains more or less melanosomes than the normal skin of the individual exhibiting mosaicism.