多重性人格疾患，又名多重人格，是心理疾病的一种，常与精神分裂搞混，较早的《精神疾病诊断与统计手册》（DSM）版本将其命名为多重人格障碍（Multiple Personality Disorder，MPD），后来改名为解离性身份障碍（Dissociative Identity Disorder，DID），多重人格即具有超过一个人格存在（若只有两个则称为“双重人格”），就有如「在一个身体里住着好几个灵魂」。

长久以来，很多人包括精神科医生、心理学家、社工以为多重人格是非常之罕见的疾病，其实不然，只是由于太多临床工作者都缺乏正确认知，以致不少误诊情况，再加上一般人的讳疾忌医和迷信等等，所以很多个案都漏报、少报。正如玛莲娜·史坦伯格的《镜子里的陌生人——解离症：一种隐藏的流行病》所言，解离性障碍其实是一种隐藏了的流行病，而多重人格只是其中一型而已。

Dissociative identity disorder (DID), previously known as multiple personality disorder (MPD), is a mental disorder on the dissociative spectrum characterized by the appearance of at least two distinct and relatively enduring identities or dissociated personality states that alternately show in a person's behavior, accompanied by memory impairment for important information not explained by ordinary forgetfulness. These symptoms are not accounted for by substance abuse, seizures, other medical conditions, nor by imaginative play in children. Diagnosis is often difficult as there is considerable comorbidity with other mental disorders. Malingering should be considered if there is possible financial or forensic gain, as well as factitious disorder if help-seeking behavior is prominent.