AbstractA high‐resolution banding technique has become indispensable in the study of patients with both congenital abnormalities and malignant diseases and has been used in various fields. A small chromosomal change is hard to detect, unless a sophisticated technique is used. In the present paper, our experience of small structural changes in a chromosome in the case of Prader‐Willi syndrome, retinoblastoma and aniridia‐Wilms' tumor association are summarized and briefly reviewed in the light of current high‐resolution techniques, including the acridine orange technique developed by ou