An unusual case of paternity testing is reported in which determination of paternity was an essential part of a genetic diagnosis. A Y-chromosomal abnormality, observed in a 33-year-old male whose wife had experienced a series of spontaneous abortions, was not found in his alleged father. DNA fingerprinting with the oligonucleotide multilocus probe (CAC)5 yielded two aberrant bands for the proband, i.e. bands exhibited by neither parent. This finding resulted in a comparatively low paternity probability of 0.02934 which is suggestive of, but does not unequivocally prove, false paternity. Subsequent analysis with other multi- and single-locus systems, however, failed to confirm this preliminary result. The paternity probability computed on the basis of the single-locus systems was 0.99997, providing compelling evidence in favour of true paternity. The present case thus demonstrates that even when two mutations turn up in a DNA fingerprint, these may be readily recognized as such.