The present invention relates to a system for positioning with respect to a patient's body an observation and/or intervention device having a portion penetrating into the patient's body comprising a base disposed over the patient's body; a means for supporting the device formed of a first portion movably assembled on the base according to a connection with one degree of freedom, and of a second portion movably assembled on the first portion according to a connection with one degree of freedom and connected to the device; and means for actuating the first portion with respect to the base, and the second portion with respect to the first portion, in which the base surrounds at a distance at least partially the device, said device being detachably connected to the second portion to enable removal of the positioning system while leaving in place the device.