Amplification of oncogenes has been observed frequently in various human malignancies and might be of clinical relevance. In the last decade, the exploration of oncogene activation due to DNA amplification in cancer research has mainly focussed on three aspects: (i) the assessment of oncogene amplification as a prognostic marker for survival of cancer patients, (ii) the development of reliable methods for detection of tumors which harbor DNA amplification of oncogenes and (iii) the identification of the gene or genes responsible for the biological (prognostic) significance in tumors with DNA amplification and the characterization of these candidate proto-oncogenes that might help to elucidate their normal function and the role in tumor development. In this review, these three aspects will be highlighted with regard to DNA amplification of the chromosome 11q13 region. Chromosome 11q13 amplification has been found frequently in certain human malignancies; in cancer of the breast and of the head and neck region, amplification of this region is observed in 13 and 29% of tumors, respectively. The 11q13 amplification has been reported to be of clinical relevance in these cancers, since patients with this amplification show a poor clinical course of disease. The amplified 11q13 region is estimated to be 3-5 Mb in size and to harbor many (putative) genes. Recently, two candidate genes, CCND1 and EMS1, were identified which were both over-expressed in all carcinomas with an 11q13 amplification. Therefore, the activation of these genes might confer the selective advantage to these tumors. In addition, the characterization of these two novel genes sustained their potential role in carcinomas with 11q13 amplification.