多尿症（英文：Polyuria）是指在一定时间内，所排出的尿量比一般高。

如果饮水量为2000毫升，正常人的尿量介于800毫升－2000毫升。

如果所排出的尿量在一天内高于2500毫升，便是多尿症。

Polyuria is a condition usually defined as excessive or abnormally large production or passage of urine (greater than 2.5 or 3 L over 24 hours in adults). Frequent urination is sometimes included by definition but is nonetheless usually an accompanying symptom. Increased production and passage of urine may also be termed diuresis. Polyuria often appears in conjunction with polydipsia (increased thirst), though it is possible to have one without the other, and the latter may be a cause or an effect. Psychogenic polydipsia may lead to polyuria.