Several websites, including WebMD, Isabel and Mayo Clinic, offer free online symptom checkers. Each of these resources stress that online diagnosis is no substitution for an in-person appointment with a licensed physician, which is the most accurate and reliable way to receive a medical diagnosis.
The WebMD symptom checker walks a patient through a series of increasingly specific questions before arriving at a list of possible ailments, based on the symptoms described. Similarly, the Mayo Clinic symptom checker prompts a patient to choose from a list of common ailments and, by asking additional information regarding that condition, provides a list of possible diagnoses. Mayo Clinic's symptom checker alphabetizes its results and divides them into ailments common to adults and ailments common to children.
Isabel boasts a symptom checker used by physicians. Isabel prompts a patient to enter basic information about his ailment and then lists probable diagnoses. To learn more about these conditions, Isabel directs patients to external websites such as Wikipedia.