A medical condition is termed heterogeneous, or a heterogeneous disease, if it has several etiologies (root causes); as opposed to homogeneous conditions, which have the same root cause for all patients in a given group. Examples of heterogeneous conditions are hepatitis and diabetes. Heterogeneity is not unusual, as medical conditions are usually defined pathologically (i.e. based on the state of the patient), as in "liver inflammation", or clinically (i.e. based on the apparent symptoms of the patient), as in "excessive urination", rather than etiologically (i.e. based on the underlying cause of the symptoms). Heterogeneous conditions are often divided into endotypes based on etiology.
Where necessary to determine appropriate treatment differential diagnosis procedures are employed.