The parental origin of the additional chromosome complement in a total of 17 cases of triploidy was determined mainly using highly polymorphic microsatellites. Maternal origin of the triploidy was demonstrated in most cases. To the best of our knowledge, this is the first systematic evaluation of the parental origin of chromosome sets in fetuses who survived until a cytogenetic diagnosis was established. In contrast to previous investigations this study documented a predominance of maternal origin of the extra haploid set mainly due to longer survival time for digynic triploidies. The concept of 2 distinct fetal phenotypes in triploidy is clearly supported by this study. (C) 1995 Wiley-Liss, Inc.