在医学中，鉴别诊断指的是将某个特定疾病从其他展现类似症状的疾病中区分开来。医师对病患作鉴别诊断，诊断特定的疾病，或着至少消除立即致命的情况。有时每个可能的病因都被称为一个鉴别诊断（例如：在评估咳嗽时，支气管炎可能是一个鉴别诊断，但最终的诊断是流行性感冒）。

更一般的说，鉴别诊断进程是一种系统化的诊断方法，将某个原因从其他多个选择中辨识出来。这种方法本质上是消去的过程，或着是将其他选择的可信机率缩减到可以忽略的程度。使用的证据包括症状、家族病史、医学知识，用以调整各种病因的可信度。

In medicine, a differential diagnosis is the distinguishing of a particular disease or condition from others that present similar symptoms. Differential diagnostic procedures are used by physicians and other trained medical professionals to diagnose the specific disease in a patient, or, at least, to eliminate any imminently life-threatening conditions. Often each individual option of a possible disease is called a differential diagnosis (for example, bronchitis could be a differential diagnosis in the evaluation of a cough that ends up with a final diagnosis of common cold).