What's known on the subject? and What does the study add? The sensitivity of the foreskin and its importance in erogenous sensitivity is widely debated and controversial. This is part of the actual public debate on circumcision for non-medical reason. Today some studies on the effect of circumcision on sexual function are available. However they vary widely in outcome. The present study shows in a large cohort of men, based on self-assessment, that the foreskin has erogenous sensitivity. It is shown that the foreskin is more sensitive than the uncircumcised glans mucosa, which means that after circumcision genital sensitivity is lost. In the debate on clitoral surgery the proven loss of sensitivity has been the strongest argument to change medical practice. In the present study there is strong evidence on the erogenous sensitivity of the foreskin. This knowledge hopefully can help doctors and patients in their decision on circumcision for non-medical reason. Objectives: To test the hypothesis that sensitivity of the foreskin is a substantial part of male penile sensitivity. To determine the effects of male circumcision on penile sensitivity in a large sample. Subjects and Methods: The study aimed at a sample size of ?1000 men. Given the intimate nature of the questions and the intended large sample size, the authors decided to create an online survey. Respondents were recruited by means of leaflets and advertising. Results: The analysis sample consisted of 1059 uncircumcised and 310 circumcised men. For the glans penis, circumcised men reported decreased sexual pleasure and lower orgasm intensity. They also stated more effort was required to achieve orgasm, and a higher percentage of them experienced unusual sensations (burning, prickling, itching, or tingling and numbness of the glans penis). For the penile shaft a higher percentage of circumcised men described discomfort and pain, numbness and unusual sensations. In comparison to men circumcised before puberty, men circumcised during adolescence or later indicated less sexual pleasure at the glans penis, and a higher percentage of them reported discomfort or pain and unusual sensations at the penile shaft. Conclusions: This study confirms the importance of the foreskin for penile sensitivity, overall sexual satisfaction, and penile functioning. Furthermore, this study shows that a higher percentage of circumcised men experience discomfort or pain and unusual sensations as compared with the uncircumcised population. Before circumcision without medical indication, adult men, and parents considering circumcision of their sons, should be informed of the importance of the foreskin in male sexuality.