The morphological normality of a spermatozoon is considered to be an important factor in relation to its ability to fertilize an oocyte. We examined the influence of morphology (strict criteria) on the rates of fertilization, pregnancy and spontaneous abortion obtained following conventional in-vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in our clinical programme. We found our fertilization cut-off values for conventional IVF to be slightly different from those of the Kruger group (10 and 5%, compared to 14 and 5%). We also found the pregnancy rate per transfer to be as good or better in the groups with < 5% normal forms: 36% of these men had a fertilization rate > 50% using conventional IVF, showing that fertilization capacity is not necessarily impaired even in this 'poor prognosis' group. With the exception of the ICSI group with 5-9% normal forms, the rate of spontaneous abortion in this study was similar to or lower than in our IVF/ICSI programme overall. When the 5-9% normal spermatozoa group was divided into those with teratozoospermia as the only factor and those with additional sperm factors, the increased abortion rate was found in the group with multiple sperm factors (67% spontaneous abortions).