精神疾患(mental disorder)
任何有关心理原因的病症，外在表现为情绪失调症候群或异常行为。绝大部分的精神疾患，都可以广义分为精神病（psychosis）和精神官能症（neurosis）两种。其中，精神病是主要的、症状较严重的精神疾患，患者会有错觉（delusions）、幻想（hallucinations）、失去现实感等，例如精神分裂症（schizophrenia）或双重人格（bipolar disorder）等。至於精神官能症则是症状较轻微、容易治癒的精神疾患，包括忧郁（depression）、焦虑（anxiety）、偏执狂（paranoia）、强迫症（obsessive-compulsive disorders）及创伤後压力症候群（post-traumatic stress disorders）等。某些心理疾症明显是导因於大脑组织的病变，例如阿兹海默症，但是绝大部分这类疾病的致病机转，医界仍然不知道知或未能证明。另外，精神分裂症也有一部分是导因於遗传基因。一些情绪上的疾病，例如狂躁（mania）或忧郁（depression），则可能是因为大脑中的某些神经传导素（neurotransmitters）失衡所致，这些大都可以藉由药物来矫治（参阅psychopharmacology）。精神官能症也常是因为心理因素引起的，例如情绪性剥夺感、挫折感、或是童年受凌虐经验；这类大都可透过心理治疗（psychotherapy）来医治。某些精神官能症，尤其是焦虑疾病中的恐慌症（phobias），则可能成为人类对制约反射的等化物，而表现出适应不良的反应。
English version：
mental disorder
Any illness with a psychological origin, manifested either in symptoms of emotional distress or in abnormal behavior. Most mental disorders can be broadly classified as either psychoses or neuroses (see neurosis, psychosis). Psychoses (e.g., schizophrenia and bipolar disorder) are major mental illnesses characterized by such severe symptoms as delusions, hallucinations, and inability to objectively evaluate reality. Neuroses are less severe and more treatable illnesses, including depression, anxiety, and paranoia as well as obsessive-compulsive disorders and post-traumatic stress disorders. Some mental disorders, such as Alzheimer's disease, are clearly caused by organic disease of the brain, but the causes of most others are either unknown or not yet verified. Schizophrenia appears to be partly caused by inherited genetic factors. Some mood disorders, such as mania and depression, may be caused by imbalances of certain neurotransmitters in the brain; they are treatable by drugs that act to correct these imbalances (see psychopharmacology). Neuroses often appear to be caused by psychological factors such as emotional deprivation, frustration, or abuse during childhood, and they may be treated through psychotherapy. Certain neuroses, particularly the anxiety disorders known as phobias, may represent maladaptive responses built up into the human equivalent of conditioned reflexes.