The authors present the case of a child with partial trisomy of the long arm of chromosome 6 who was observed aged between 1 and 5 months and 5 years and 5 months. The kariotype shows a duplication of the distal tract (6q22.36-->qter) deriving from the imbalance of a maternal malsegregation. The phenotype is that characteristic of the syndrome: microbrachycephalia with a high and prominent forehead, "full" orbits, exophthalmos, antimongoloid palperbral fissures, hypertelorism, flattened root of the nose, antiverted nostrils, small mouth with thin lips, micrognathy, auricles with a low implantation, short and thick neck with anterior palmature, low implantation of hair at nape, reduced diameter of chest, articular retraction, clinodactilia of 5th finger, bilateral single palmar groove, hypospadia. Weight, height and cranial circumference were below the 3rd percentile. The cases of dup (6q) reported in the literature generally describe similar somatic characteristics so much so that these may represent a syndrome. However, there is considerable variation in the level of visceral and cerebral impairment, only partly attributable to the degree of chromosome imbalance. The general conditions of the probabd were good and there was no malformation of internal organs. Magnetic resonance scan of the brain showed a slight increase in the volume of the ventricular system and a slight dilatation of the subarachnoid spaces with a dysmorphic cortical pattern.(ABSTRACT TRUNCATED AT 250 WORDS)