Karyotype and FISH with Y chromosome specific probe of a 'girl' with isodicentric Y chromosome. 'She' (aged 20 months old) presented with ambiguous genitalia (enlarged phallus, no palpable testis). 'She' had functioning test revealed by HCG test. The results of cytogenetic analysis showed mos 45,X/46,X,idic(Y)(p11.32) karyotype and nuc ish (DXZ1x1)//(DXZ1x2)//(DXZ1,DYZ3)x1//(DXZ1x2,DYZ3x1)//(DXZ1x1,DYZ3x2)//(DXZ1x2,DYZ3x2)//(DXZ1x1,DYZ3x3). Panel A shows the 46,X,idic(Y)(p11.32) karyotype and Panel B indicates the Y chromosome signals, which always appears side by side in some cells.