A medical procedure and a system are provided so that two visions are obtainable through natural orifices by means of two observational apparatuses, or one the two visions is selectable. The medical procedure through a natural orifice comprises: forming an orifice in a hollow organ by using a device inserted into the hollow organ from a natural orifice of a patient; introducing a first observation device from said orifice formed in said hollow organ into an abdominal cavity; introducing a second observation device from said orifice formed in said hollow organ into the abdominal cavity; arranging said second observation device in a position different from that of said first observation device; simultaneously or selectively displaying an image obtained from said first observation device and an image obtained from said second observation device; and performing a desired procedure in the abdominal cavity while confirming the images.