The correlation between the morphology of human sperm and their in- vitro fertilizing capacity was assessed using three classification systems. All the experiments were conducted in an in-vitro fertilization clinic. Semen samples obtained were air dried, stained and mounted on microscope slides. They were then evaluated by a modified Williams system, the World Health Organization (WHO) guidelines, and a morphometric system. These observations were correlated with the actual success of fertilization by the sperm from the same man in in-vitro fertilization trials. Based on statistical analyses, the number of amorphous cells was the only reliable predictor of fertility. In both the Williams system and the WHO system, the amorphous head shape best predicted fertility, correctly predicting the fertility status in 65 percent of the cases. The next best predictor of fertility was the normal morphology of sperm, but only in the modified Williams system and not in the WHO system. The authors conclude that the morphology of sperm, as the sole criterion, does not predict fertility in man.