Analysis of fetal mortality in sibships of 406 probands with cleft lip with or without cleft palate (CL(P)) indicates that the incidence of fetal mortality is significantly greater in sibships of probands with bilateral CL(P) than in those of unilateral CL(P). The difference is even greater when fetal mortality in sibships of male probands with unilateral CL(P) is compared with that of female probands with bilateral CL(P). These findings support a multifactorial two‐threshold concept in which a lower level of liability results in clefting while a higher level of liability causes fetal mortalit