We report an innovative fluorescence in situ hybridization technique which exploits a unique resource of 41 telomere-specific probes and allows the simultaneous analysis of the subtelomeric region of every chromosome for deletion, triplication and balanced translocation events. This technique requires only a single microscope slide per patient and is expected to be a useful diagnostic tool with applications in the fields of idiopathic mental retardation, the detection of congenital abnormalities and in some forms of cancer. This will lead to more accurate genetic counselling of patients and their families and will provide the basis for future diagnostic, therapeutic and preventative measures.