We report a 2-year-old boy with Prader-Willi Syndrome (PWS) caused by a deletion of the PWS critical region as a result of an unbalanced translocation t(3;15). Additional features, including central visual impairment, relative macrocephaly, retrognathia, preauricular tags, and bilateral club-feet, were noticed. The extension of the deletion was determined by fluorescence in situ hybridization (FISH) analysis using 11 region-specific YAC clones. Nine YACs were found to be deleted, allowing us to determine that the deletion is larger than in patients with typical PWS deletions. The karyotype of this patient can thus be designated: 45,XY,-15,der(3)t(3;15)(qter;q14).ish der(3)t(3;15)(qter;q14) (wcp3+,wcp15+,D15S10-,PML+,D15Z1-,D3S4560+,801_f_9x1, 815_e_6x2) de novo. Molecular analyses using seven polymorphic markers helped to narrow down the breakpoint between marker ACTC.PC3 and the distal end of the YAC 815_e_6. These results provide evidence that haploinsufficiency for genes in 15q13-q14, not affected in common PWS deletions, is associated with the additional features found in the patient, including a central visual impairment.