The medical history, case history, or anamnesis (from Greek: ἀνά, aná, "open", and μνήσις, mnesis, "memory") of a patient is a set of information the physicians collect over medical interviews. It involves the patient, and eventually people close to him, so to collect reliable/objective information for managing the medical diagnosis and proposing efficient medical treatments. The medically relevant complaints reported by the patient or others familiar with the patient are referred to as symptoms, in contrast with clinical signs, which are ascertained by direct examination on the part of medical personnel. Most health encounters will result in some form of history being taken. Medical histories vary in their depth and focus. For example, an ambulance paramedic would typically limit their history to important details, such as name, history of presenting complaint, allergies, etc. In contrast, a psychiatric history is frequently lengthy and in depth, as many details about the patient's life are relevant to formulating a management plan for a psychiatric illness.

The information obtained in this way, together with the physical examination, enables the physician and other health professionals to form a diagnosis and treatment plan. If a diagnosis cannot be made, a provisional diagnosis may be formulated, and other possibilities (the differential diagnoses) may be added, listed in order of likelihood by convention. The treatment plan may then include further investigations to clarify the diagnosis.

The method by which doctors gather information about a patient's past and present medical condition in order to make informed clinical decisions is called the history and physical (a.k.a. the H&P). The history requires that a clinician be skilled in asking appropriate and relevant questions that can provide them with some insight as to what the patient may be experiencing. The standardized format for the history starts with the chief concern (why is the patient in the clinic or hospital?) followed by the history of present illness (to characterize the nature of the symptom(s) or concern(s)), the past medical history, the past surgical history, the family history, the social history, their medications, their allergies, and a review of systems (where a comprehensive inquiry of symptoms potentially affecting the rest of the body is briefly performed to ensure nothing serious has been missed). After all of the important history questions have been asked, a focused physical exam (meaning one that only involves what is relevant to the chief concern) is usually done. Based on the information obtained from the H&P, lab and imaging tests are ordered and medical or surgical treatment is administered as necessary.