Editor—In the October 2000 issue of the journal, five new cases of unbalanced translocations with partial monosomy 4p and partial trisomy 8p were described by Wieczorek et al 1 and the authors concluded that de novo translocations causing Wolf-Hirschhorn syndrome (WHS) are more frequent than previously estimated. In particular, unbalanced de novo translocations involving the short arms of chromosomes 4 and 8 seem to be frequent in WHS patients. Furthermore, because of the limited resolution of cytogenetic techniques, some cryptic translocations can be missed by routinely performed cytogenetic differential diagnosis. Therefore, the authors emphasised the necessity of investigating all patients with WHS and visible chromosomal imbalances in chromosome 4p by fluorescence in situ hybridisation (FISH), using a chromosome 4 specific painting probe (whole chromosome painting, wcp) to detect possible translocations. Here we report on two further cases with unbalanced de novo translocations t(4;8). The unbalanced translocation was not detectable by conventional cytogenetics alone and was also not detectable just by painting with a chromosome 4 specific library. We have chosen a different strategy using the comparative genomic hybridisation (CGH) technique as a straightforward molecular cytogenetic assay to unravel unbalanced chromosomal translocations. Subsequently, the CGH results were confirmed by FISH.