Advances in the treatment of congenital heart disease (CHD) have increased life expectancy, entailing medical surveillance for a considerable number of adolescents and young adults with CHD for issues arising in areas such as sexual health. This study aimed to assess the sexual knowledge and the needs for sexual health education among this group. The participants comprised 53 young adult outpatients (27 males, median age: 23 years) who had undergone surgical interventions (median: 3 times) for CHD. The Knowledge related to Safe Sex Practice scale (KSSP), an assessment tool containing 15 questions on sexual knowledge, was administered, and the rates of correct answers for each item and the overall scale were compared with the age and sex of a control group (n = 164). The overall mean KSSP score of the participant group (10.5 ± 1.8) was significantly lower than that of the control group (11.1 ± 1.9, p = .035). The KSSP scores of the participants with low peripheral oxygen saturation (SaO2 < 95%) were significantly lower (9.77 ± 1.85) than those with normal SaO2 (11.06 ± 1.85, p = .009). Regarding sexual health education, the participants reported receiving information about contraception as more important than other areas of sexual health. The rate of incorrect answers was higher for questions regarding natural ways of contraception utilizing infertile periods in the menstrual cycle. Based on an informed understanding of those with CHD, healthcare providers in this field should develop customized sexual health education for adolescents and young adults with CHD and implement customized sexual health education, including effective contraception methods.