Since intracytoplasmic sperm injection (ICSI) has been introduced in the techniques for the non-causal treatment of severe male factor infertility failure of conventional in-vitro fertilisation and subsequent embryo transfer due to failed oocyte-fertilisation has become rare in these cases. Nonetheless, even in ICSI cycles cases occur where no transfer can be performed for several reasons. The contribution of sperm-, oocyte- and other factors are reviewed in this article. 78 (5.4%) out of 1433 ICSI cycles, performed from 1.1.1995 up to 31.5.1997, in which no transfer could be done, despite a performed follicular puncture, were used as an example. 30 cycles with no fertilisation, 17 with no oocytes, 8 with only degenerated oocytes retrieved, 17 with no injectable sperms, 4 with no normal fertilisation, and 2 with no cleavage after normal fertilisation were identified. In more than two thirds of the cases an oocyte factor, identified by a high FSH, low response to the hormonal stimulation or no fertilization despite the presence of motile sperms, was present. The other cases were attributed to a sperm factor or other causes. After one failed ICSI cycle - i.e. a cycle with no embryo transfer - the chance to conceive is very low in a subsequent cycle. Only 1 out of 24 cycles was successful in terms of an established and ongoing pregnancy.