Chromosome analysis was performed in a 34-year-old man who was phenotypically normal except for oligoasthenozoospermia. In this patient, analysis of GTG-banded chromosomes showed in one chromosome 8 additional chromosomal material of unknown origin. To characterize the aberrant chromosome more precisely, a paint specific for chromosome region 8pter-->8p23.1 was generated by microdissection and degenerated oligonucleotide primed-polymerase chain reaction (DOP-PCR) and used as fluorescence in situ hybridization (FISH) paint. After reverse painting, hybridization signals were only found on the short arm of the two chromosomes 8, with an enlarged signal on the derivative chromosome 8. The duplication was characterized further with band-specific FISH probes. We concluded that (part of) chromosome region 8p23.1-->p23.3 was duplicated. Chromosome analysis of the parents showed that the dup(8) was of maternal origin and that the fertile brother of the index patient also was a carrier of the chromosome aberration. There was no history of miscarriages. We suggest that duplication of region 8p23.1-->p23.3 can be regarded as euchromatic variant or duplication with no phenotypic effect.