性偏离（英语：paraphilia），或称性反常(sexual perversion)、性心理异常（psychosexual disorder）、性变态(sexual deviation)等，也有性欲倒错或性倒错、性偏好障碍之说，是一系列心理卫生名词，指对于特定人、事、物产生性欲的事物或情况产生性渴望的偏好。并非所有的性偏好都是精神疾病（Mental disorder），因此，必须将「性偏好障碍」与「性偏好」做定义上的区分。性偏好障碍的定义必须在该性偏好出现导致个人痛苦或损伤，以及性满足涉及伤害自己或他人。意即，性偏好是性偏好障碍的必要但非充分条件，性偏好本身非属临床必要介入的理由。

Paraphilia (also known as sexual perversion and sexual deviation) is the experience of intense sexual arousal to atypical objects, situations, or individuals. No consensus has been found for any precise border between unusual sexual interests and paraphilic ones. There is debate over which, if any, of the paraphilias should be listed in diagnostic manuals, such as the Diagnostic and Statistical Manual of Mental Disorders (DSM) or the International Classification of Diseases (ICD).