In this study we have defined the changes in gene copy number of the candidate oncogene ZNF217 during colon cancer development and progression. This gene is mapped to chromosome 20q and lies within 20q13.2, a region which we have previously shown to be highly amplified in colorectal cancer by comparative genomic hybridization. The gene copy number of ZNF217 was assessed in 100 colon carcinomas (19 Dukes' A, 42 Dukes' B and 39 Dukes' C), 13 colonic adenomas and 10 normal colon samples. DNA extracted from laser microdissected cells was amplified by multiplex real-time PCR at two distinct gene loci—ZNF217 and β-globin (control gene)—on an ABI7700 sequence detection system. Of the 100 colon cancers studied, 61 showed some level of amplification of ZNF217, 15 had loss of ZNF217, while 24 were diploid. All the adenomas except one were diploid. In this study we have found that ZNF217 amplification is a frequent event in colon cancer and that the extent of its amplification varies markedly between tumours (range 3–13 copies). There was a trend toward poorer survival in patients whose cancers had either gain or loss of ZNF217. Copyright © 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.