A 36-year-old single woman presented at the out-patient clinic in March 2000 requesting donor insemination. Between May 2000 and May 2001 she underwent six cycles of intrauterine insemination with donor sperm after clomiphene citrate stimulation without achieving a pregnancy. In January 2002, ICSI was performed; two embryos were transferred on day 3 and a dizygotic bichorionic pregnancy was achieved, which ended in a miscarriage at 21 weeks of gestation. After a second unsuccessful ICSI attempt in which a single embryo transfer was performed, she embarked upon her third attempt in March 2003 at 39 years of age. Two blastocysts were transferred after ICSI, resulting in a quintuplet gestation consisting of a monochorionic biamniotic pregnancy and a monochorionic triamniotic pregnancy. The current case report indicates that monozygotic pregnancies consisting of both twins and triplets are possible after treatment by assisted reproductive technologies. An association between extended culture, manipulation of the zona pellucida, ovarian stimulation and occurrence of monozygotic pregnancies has been suggested by retrospective studies. However, in order to identify more reliably predictive factors for the occurrence of monozygotic pregnancies, it is necessary to perform prospective trials.