An excess of structural defects occurs in monozygotic twins compared to dizygotic twins or singletons. Among these defects the acardius acephalus or chorangiopagus parasiticus is one of the most rare and severe and a possible cause of pathology to the other twin. Ovulation induction by clomiphene causes an increased frequency of multiple gestation and possibly of monozygotic multiple pregnancy. In the present report, we describe a prenatally diagnosed and autopsied case of acardius acephalus from a pregnancy established after ovulation induction by clomiphene. Approximately 1.4% of pregnancies are accomplished after use of ovulation inducing medication in the Netherlands. A possible etiological role of clomiphene justifies close monitoring of future cases. © 1993 Wiley‐Liss, Inc.