Observation services are short-term  outpatient  services you received when you are in the hospital. You usually have this for monitoring purposes and/or to determine whether you should be admitted as an  inpatient .  It is important to know that if you are receiving observation services, you haven't been formally admitted to the hospital as an inpatient, even if you are given a room or to stay overnight.  You can always ask the hospital staff about your status. Also, the hospital must provide you with a notice if you receive observation services for more than 24 hours. This is called the  Medicare  Outpatient Observation Notice (MOON) . This notifies you that you are receiving observation services. This explains why you are an outpatient and your doctor should explain this notice to you in person. Since this kind of service often involves an overnight stay in the hospital, they may look no different than inpatient services. However, it is very impor...