Understanding the genes and genetic pathways targeted by recurrent chromosomal imbalances in malignancy, along with the molecular mechanisms that generate the imbalances, are important problems in cancer biology. In this report, we demonstrate that oligonucleotide array CGH (oaCGH) analysis can routinely map chromosomal imbalance breakpoints at exon‐level resolution, including imbalances that are single copy number genomic alterations. Different tiling‐path array designs were used in this study: a whole‐genome array with a 6‐kb median probe spacing and fine‐tiling arrays for selected genomic regions with either 50‐ or 140‐bp median probe spacing. In both array formats, oligonucleotide probes were of isothermal design and were tiled through genic and inter‐genic regions. Whole‐genome oaCGH analysis of two neuroblastoma cell lines and three primary tumors led to the identification of 58 chromosomal breakpoints that generated 45 large‐scale partial chromosomal imbalances (>2 Mb). An unexpectedly high proportion (34%) of these breakpoint intervals mapped to regions containing segmental duplications. In addition, 88 smaller‐sized regions (<2 Mb) of imbalance were detected, the majority of which mapped to segmentally duplicated regions and may reflect constitutional copy number polymorphisms. The chromosomal breakpoints for 12 recurrent abnormalities exhibited in neuroblastoma tumors and cell lines, including MYCN amplicon boundaries, loss of 3p, loss of 11q, and gain of 17q, could be mapped to intervals ranging from 50 bp to 10 kb in size using high‐density fine‐tiling oligonucleotide microarrays. Fine‐tiling oaCGH analysis provides an unprecedented level of resolution, allowing detailed mapping of recurrent unbalanced chromosomal abnormalities. Supplementary material for this article can be found on the Genes, Chromosomes, and Cancer website at http://www.interscience.wiley.com/jpages/1045‐2257/suppmat/index.html. © 2005 Wiley‐Liss, Inc.