How to understand the erectile function? How to define erectile dysfunction? In general, erectile function is evaluated by the quality of penile erection.If penis shows good erection, we think erectile function is normal.Otherwise, erectile dysfunction occurs.This concept is reflected in the definition of erectile dysfunction (ED).ED is defined as the persistent inability to attain and maintain an erection sufficient to permit satisfactory sexual performance.From the definition of ED, it is comprehensible that the penile erection is only related to the hardness of penile erection.Therefore, if the hardness of penile erection is sufficient to complete a satisfactory sexual intercourse, we could consider the erectile function is normal.Conversely, if the hardness of penile erection is not enough, erectile dysfunction is indicated.However, sometimes we meet the following kinds of patients in clinics.Firsdy, the patients who are diagnosed as phallocampsis.The morphology of penis is flexural after erection: upward bending, down bending, left bending, right bending, S-shaped curve or rotating, et al.Secondly, in some patients, proximal part of penis is much more slender than glans, like a spindle.Full erection could be achieved in these patients without any abnormalities indicated by nocturnal penile tumescence (NPT) test, intracavernous pressure (ICP) measurement and color duplex ultrasonography.But the penis is very easy to swing during the sexual intercourse and the stability of penile erection is abnormal.