A number of unresolved issues in sexology research and practice are reviewed. Penile volume assessment of sexual arousal has consistently proved more sensitive than penile circumference assessment and requires much shorter exposure to the erotic stimuli eliciting the arousal, reducing the subjects' ability to modify their responses. Failure to acknowledge this has allowed acceptance of evidence based on penile circumference assessment that behavioral treatments such as directed masturbation can increase the ability of sex offenders to be heterosexually aroused and aversive therapy can reduce their deviant urges whereas penile volume assessment indicates these procedures are ineffective. A randomized controlled trial of relapse prevention versus no treatment for sex offenders found more treated than untreated subjects reoffended after a mean follow-up period of 4 years. Researchers and therapists accepted that a post hoc statistical manipulation of the results provided evidence of a treatment effect. Subsequently it has been recommended that randomized controlled evaluations of treatments of sex offenders be abandoned. Meta-analysis of outcome studies has been used uncritically. The majority of men and women who report homosexual feelings and/or behavior report predominant heterosexual feelings and behavior and do not identify as homosexual. These consistent findings remain ignored. Studies of the etiology and development of homosexuality and heterosexuality treat them as distributed categorically rather than dimensionally and investigate only self-identified homosexuals and heterosexuals. With this methodology the predominantly heterosexual majority are excluded or misclassified. The belief that the European concept of the homosexual is a late 19th-century invention is based on an inadequate reading of literature. Limitations of the DSM classification of sexual and gender identity disorders are pointed out. The validity of self-report of sexual behavior has been questioned on the basis that men report a markedly higher average number of sexual partners than women. Possible sex differences in reporting the number of partners who are of the same sex, casual, or perpetrators or victims of sexual coercion and child abuse have not been taken into account. Failure of sexology to progress due to lack of resolution of conflicting issues may contribute to the low impact factor of its journals.