A prospective randomized study was conducted to assess the prognostic value of sperm morphology in an in-vitro fertilization (IVF) programme, using strict criteria. The first group (T, teratozoospermic) included 32 couples with an isolated teratozoospermia in the male partner (morphology < 9% normal). The second group (C, control) contained 36 couples with normal semen parameters, including morphology (> 9% normal, strict criteria). In both groups, 50 IVF cycles were performed. Patients were matched for indication for IVF. There was no difference between the two groups regarding age, duration of infertility, stimulation protocol, catheter used for embryo transfer and different sperm parameters. A statistically significant difference between the T and C groups respectively was observed regarding the fertilization rate (69.2 and 79.4%, P < 0.05), pregnancy rate per cycle (12.0 and 42%, P < 0.001), the pregnancy rate per transfer (13.9 and 42.0%, P < 0.01) and per embryo transferred (6.1 and 14.8%, P < 0.05). No pregnancy occurred in the poor prognosis group (morphology < 5% normal). In cases of moderate teratozoospermia, the fertilization rate appeared normal (78.6%) but the conception rate remained low. We concluded that the use of strict criteria in the assessment of sperm morphology is useful in predicting fertilization and pregnancy rate in the human in-vitro model.