Abstract: A medical diagnosis decision support system for assisting a health professional to diagnose a medical condition. The system is first provided with an anchor condition that can be a symptom, a sign, a laboratory test result, or an imaging test results or any combination thereof The system then guides users in a series of predetermined phases regarding abstract or concrete diagnosis groups that should be considered and appropriate data that should be collected during the clinical investigation process. The system suggests history and physical examination clinical data items, laboratory, and imaging tests that should be collected in order to differentiate among alternative diagnoses. In each phase, possible diagnoses are listed and ranked.