Analysis of interviews obtained from a random sample of 930 adult women in San Francisco revealed that 17% or one out of approximately every six women who had a stepfather as a principal figure in her childhood years, was sexually abused by him. The comparable figures for biological fathers were 2% or one out of approximately 40 women. In addition, when a distinction was made between Very Serious Sexual Abuse (including experiences ranging from forced penile-vaginal penetration to non-forceful attempted fellatio, cunnilingus, and anal intercourse) and other less serious forms, 47% of the cases of sexual abuse by stepfathers were at the Very Serious level of violation compared with 26% by biological fathers. Possible explanations for these startling discrepancies are discussed, and some of the implications for remarriage are considered.