A new case of interstitial deletion of the long arm of one chromosome No. 5 (q13 leads to q22) is described. The girl shows mental retardation, severe hypotonia, dysmorphic facies and peculiar dermatoglyphics. The relationship between partial trisomies and partial monosomies of 5q chromosomal segments and associated clinical features is discussed. It seems possible to draw a rough phenotypic map of the long arm of chromosome 5 (5q), correlating observed malformations and phenotypic features with specific chromosomal regions.