Medical Astrology is the branch of astrology that deals with the workings of the human body.  A competent medical astrologer can analyze a person's birth chart and determine bodily strengths and weaknesses, proneness to various disease states, and nutritional deficiencies. In the event of  illness or disease, a medical astrologer will use predictive methods to try to determine the severity and duration of the disease. Sometimes a medical astrologer can help determine the course of a disease by the use of a chart called a decumbiture chart. 

This type of astrology has its basis in ancient  astrology when the astrologer rarely knew the exact  time of birth of a subject.  Instead, a chart was set up for the time the patient "took to his bed" or for the time the physician analyzed the urine of the patient. Nowadays, the decumbiture chart can be set up for the time of a diagnosis by a doctor or for the time a person "takes to his bed." 

Medical astrology is also helpful in elective surgery. The medical astrologer can pick the best date(s) and time(s) for an elective procedure -- anything from a face lift to a college injection.  Although it is always best to have the time of  birth of the person, if this is not possible, the medical astrologer can  still help the client pick the most fortunate  times for the procedure. 

Needless to say, one should not try to use elective astrology in a medical emergency. Medical astrology should not be used to diagnose illness.  The only person who can diagnose illness is a medical doctor.  And even a medical doctor who is also versed in medical astrology would not try to diagnose illness from a birth chart.  

You may be able to determine a tendency toward various types of illnesses, and you can usually see periods of stress or lowered vitality when one could have health problems; but it is not possible nor should one attempt to diagnose illness from the birth chart. 

However, once a medical doctor has diagnoses a particular illness, the medical astrologer may be able to ascertain from the birth chart the severity or duration of the illness.  It is always helpful to know exactly when an illness began or was diagnosed as then the medical astrologer can ascertain what planetary influences the client was under at that time.  And as stated previously, if the moment of the diagnosis is recorded, a medical astrologer can set up a decumbiture chart for that time and gain more information about the course the illness.