The authors investigated three probable reasons why parents of mentally retarded children would be opposed to sex education being offered as a school subject: general sexual attitudes, specific sexual attitudes, and prejudices against the retarded child's own sexuality. A questionnnaire was given to 60 parents of retarded children and 62 parents of nonretarded children. A correlation analysis revealed evidence of all three kinds of reasons and led to a causal model of conservatism on sex education. A path analysis revealed that (a) sexual prejudices are a major obstacle to sex education, and (b) each group of parents represents a specific dynamic of conservatism on sex education. Means of pedagogical intervention to modify parents' attitudes toward sex education of handicapped children were discussed.