While case seriesCase series are low in the hierarchy of evidenceHierarchy of evidence, they remain the most common study reported in the surgical literature. A number of case series have reported landmark interventionsIntervention or disease classifications for surgeons, and they remain popular in reporting rare cases and novel procedures. They have high external validityValidity and are fast and cheap to perform. Case series can be used to prepare for a higher level study by demonstrating feasibility and establishing patient and outcomeOutcomes parameters. Alone, they are sufficient to establish an intervention’s safety and a test’s diagnostic accuracy. However, case series lack a control group by definition and are commonly performed with a retrospective design. It is important for surgeons to be familiar with their appraisalAppraisal. This chapter provides a guideGuide to readers on evaluating a case seriesCase series in surgerySurgery.