GERMAN recently suggested that the high prevalence of Down's syndrome among the children of older mothers results from relatively low frequencies of sexual intercourse among such mothers and a consequent increase in the probability of delay in fertilization of discharged ova1. To test this hypothesis, he suggested that the prevalence of Down's syndrome be studied among the offspring of unmarried mothers, “who as a group engage in coitus sporadically rather than systematically”. On similar grounds, Goodhart2 postulated that a particularly high prevalence should be expected in the children of young unmarried mothers.