Intracytoplasmic sperm injection (ICSI) is the latest of several microfertilization techniques that have been utilized predominantly to overcome severe male subfertility, giving fertilization and term pregnancy rates similar to conventional in-vitro fertilization (IVF) (but for other indications). Even though available data on children born after ICSI are very encouraging, the procedure must still be considered as novel and the safety aspect to a great extent unexplored. In our opinion, therefore, ICSI should only be used for specific indications, and in this communication the non-existent, relative and absolute indications for performing ICSI are outlined and discussed. With an apparently normal sperm sample, ICSI should not be used in a first cycle even if only few oocytes are obtained. When there is reason to suspect poor fertilization, ICSI can be used in combination with conventional IVF in a split cycle. This includes cases of 'subnormal' sperm samples, high titres of antisperm antibodies, or following a single cycle of poor fertilization using conventional IVF. Absolute indications for ICSI include two previous fertilization failures with conventional IVF, use of epidiymal or testicular sperm samples, or when only acrosomeless or immotile spermatozoa are available. The fertilization of oocytes prior to preimplantation genetic diagnosis is another absolute indication. It is, however, important to keep in mind that for this novel technique, indications should not be rigid, but remain variable with respect to new findings.