Abstract: An improved method and apparatus for automatically controlling the direction of advance of a rotary drill to produce a borehole profile substantially as preplanned with minimal curvature while maintaining optimum drilling performance. The preferred embodiment of the system comprises a drill string; a drill bit; an appropriate motor for rotating said drill bit; a data processing system for storing a planned path; sensors for obtaining information for providing a profile of a drilled path of the borehole; a data processing system for comparing the drilled path with the planned path and for generating a correction signal representing the difference between the drilled path and the planned path; and a control system responsive to the correction signal to cause the drill string to follow a corrected path to cause the drilled borehole to coincide with the planned path.