We report the case of a XXY boy who presents progressive neurological disorder which has started around eleven months of age, with developmental stagnation followed by regression. The child presents as well stereotypic hand movements, loss of purposeful hands use and microcephalia. Presence of any defined systemic or neurological condition which could be pointed out as the possible etiological factor for the case was not found out by investigations. It deals with a boy with phenotypic alterations very similar to those considered typical for Rett syndrome which associated with chromosomal alteration (XYY karotype) constitute evident scientific interest.