Older paternal age has been recognized as a factor in fresh gene mutations and has been documented in sporadic cases of 5 autosomal dominant conditions. In this collaborative study, an older paternal age factor was additionally documented in sporadic cases of the Basal Cell Nevus syndrome, the Crouzon syndrome, and the Waardenburg syndrome, 3 conditions in which autosomal dominant inheritance has been implied; and in sporadic cases of Acrodysostosis and Progeria, suggesting a fresh mutant gene etiology for these 2 conditions in which the mode of inheritance has been unknown. Paternal age data from a number of other disorders showed inconclusive or no older paternal age factor. Recognition that older paternal age is a major factor leading to fresh gene mutation in man should be incorporated into general recommendations relative to family planning.