Embodiments of the invention include a medical device for accessing a patient's body portion and used for diagnosis and treatment of medical conditions. Embodiments of the invention may include a particular endoscopic positioning mechanism for placing an endoscope and an additional treatment device within desired body portions in order to assist in diagnosis and treatment of anatomical diseases and disorders. In particular, a medical device according to an embodiment of the invention includes a positioning mechanism configured to maintain the relative position of a treatment instrument with respect to an underlying endoscope during a treatment procedure.