The effects of maternal age on the quality of offspring are well known. Those due to the father's age are less obvious, apart from the role of increasing paternal age in the onset of many dominant autosomal disorders. But an experimental model has demonstrated that, in rats, increasing paternal age, without any other anomalies, might produce a decreased learning capacity in progeny. The object of the epidemiological investigation presented here was to verify whether this effect might also occur in man. The study involved the distribution of scores obtained in psychometric tests by 18-year-old male subjects, according to their father’s age at the time of their birth. This distribution indicated not only that increasing paternal age is accompanied by effects similar to those observed in animals, but also that very young paternal age was also related to these effects. Thus, the curve of such scores produced an inverted U-shape, with maximum scores obtained when the father was about thirty years of age. Maternal age did not appear to play a part in this event. These results pose the problem of identifying genetic and/or psychosocial factors which might have an impact on the quality of the conceptus.