Abstract Background Although the number of adults with congenital heart disease (CHD) is increasing, there is little research into the impact of CHD on sexual activity and -dysfunction. Whether and to what extent sexual function is discussed with patients in clinical practice is also unknown. Purpose To study the current knowledge level, problems, wishes and fears of adult CHD patients regarding sexual activity. Methods Patients recruited via the German National Register for Congenital Heart Defects were invited to an online survey about sexual function. Overall, 4,484 patients (2,264 female) were invited to the survey and 873 patients (502 female) participated (19.5%). Patients were divided into four groups based on the underlying CHD severity classification: simple CHD (136 patients), moderate CHD (354 patients), complex CHD (340 patients). Results 301 (35.6%) patients reported that they had very rarely or no sex at all in the six months preceding the survey (simple CHD: 25.7%, moderate CHD: 33.6%, complex CHD: 38.2%, other CHD: 39.5%). Based on the last six months, 71.2% of the surveyed male patients estimated the probability of having and maintaining an erection as high or very high (simple CHD: 85%, moderate CHD: 71.4%, complex CHD: 69.7%). In addition, 60.6% of the interviewed male patients reported to be almost always or always able to get a full erection sufficient for sexual intercourse. In contrast, 14.6% of the male patients already had erectile dysfunction, but did not discuss this issue with their physician. Overall, only 3.5% of the male patients stated that they were offered a consultation regarding erectile dysfunction by their treating physician. In contrast, 29.6% of the male patients would like to receive such counseling during routine medical examinations. In the last six months, 56.4% of the interviewed female patients, reported no difficulties with lubrication. 44% of the female patients already received advice from their physician on sexuality, contraception and pregnancy and 64.5% of the female patients would like to receive additional medical advice and information on sexuality, contraception and pregnancy in the context of routine medical check-ups. Conclusions This study reveals important issues regarding sexual function in male and female adult patients with CHD. The study reveals important gaps in counselling patients regarding sexual issues beyond contraception and pregnancy.