Abstract : A 48, XXYY Sardinian patient, born to a 46, XX mother heterozygous for the Gd Mediterranean mutant, and to a 46, XY father hemizygous for the same mutant, was found to have a mosaic distribution of G6PD(+) and G6PD(-) peripheral red blood cells. The most likely interpretation of this finding is that the propositus is an additional example of an XXYY zygote derived from a consecutive meiotic non-disjunction during paternal gametogenesis.