病例对照研究是流行病学的其中一种研究设计。它是一种较廉宜及惯常使用的流行病学研究，只需少数的研究人员（甚至只是一个）及单一的设备，且不涉及有结构的试验。它的方法是指向一系列的重要发现及先例，其可信性却有受质疑的地方，但因它过往的成功，现时广泛被医学界所接受。

病例对照研究的最大成功是由理乍得·多尔爵士及其他科学家所发现吸烟与肺癌之间的关系。多尔在大量的病例中成功证明了两者在统计上重要的关联。但怀疑者（包括烟草业人士）争辩病例对照研究根本不能证实成因，但在最近的双盲的预测研究中已确定病例对照研究的结果，而现时已接受差不多所有因肺癌而死亡的人都是因吸烟所导致的。

A case-control study is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute. Case-control studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have that condition/disease (the "cases") with patients who do not have the condition/disease but are otherwise similar (the "controls"). They require fewer resources but provide less evidence for causal inference than a randomized controlled trial.