Diagnosis is possible on a number of levels. Traditional, overall, and interrelationship types of diagnosis are differentiated. The effectiveness of the traditional diagnosis, which is used to indicate etiology of disease, to assess the effect of the disorder on structure and function, and to classify the illness, is questioned, since it usually leads to a general prognosis based on statistical probability rather than to a unique prognosis indicating specific predictions and treatments for the individual patient. The doctor, when making this kind of diagnosis, acts as an objective observer and assesses an abstract concept, the illness rather than a person, so that the traditional diagnosis is illness-centered. By including features of the patient's personality and his relationships with others, the overall diagnosis provides a more embracing overview of the individual's physical and emotional conditions. It has greater ongoing validity in description and of usefulness for treatment by centering upon the patient as an individual whose conflicts and sufferings are felt and understood. It may require lengthy interviewing, but this may be shortened in practice by focusing upon the particular aspect of the patient's world which seems central to the pathology. This focal area is often determined spontaneously through a “flash,” the mutual intuitive recognition of an important understanding between doctor and patient, leading to further diagnostic and therapeutic work. The flash establishes a climate of high emotional charge and involves both patient and doctor intrinsically in the diagnostic process and its outcome. It is one of the means by which an interrelationship diagnosis, centered on the doctor-patient relationship, may be arrived at. Truly successful treatment in general practice, and perhaps in most branches of medicine, is probably based on some form of interrelationship diagnosis, even though this diagnosis may not have been verbalized or properly conceptualized by the doctor. Case material illustrates the effectiveness of each type of diagnosis for the physician and for his patient.