A medical system and surgical instrument adapter are provided. The medical system comprises a surgical instrument carrying a distal tool configured for performing a medical procedure on a patient, an adapter having a clam-shell configuration configured for removably receiving a proximal end of the surgical instrument, and a drive unit configured for being coupled to the adapter to control the movement of the surgical instrument within at least one degree-of-freedom. The surgical instrument adapter may comprise a base portion configured for receiving a proximal end of the surgical instrument, and a clam-shell that pivots relative to the base portion between a first position that encloses the proximal end of the surgical instrument within the base portion and a second position that allows the proximal end of the surgical instrument to be removed from the base portion.