Portable manipulators are installed for operation and then removed upon completion of their task. Typical applications of portable manipulators include the inspection of nuclear reactors, inspection and repair of nuclear steam generators and asbestos removal in buildings. In such operations, it is difficult to precisely position the manipulator at a fixed location within its workplace, yet this is critical for accurate tool positioning. It can be possible, however, to position the tool tip at several points in the environment using video feedback and manual operator control of the manipulator. This provides sufficient information to determine the position and orientation of the manipulator base frame with respect to the environment, hereafter referred to as extrinsic calibration. Following extrinsic calibration, subsequent moves of the manipulator can be automated. This paper describes a closed-form method for performing extrinsic calibration by contacting the tool to a total of six places on three orthogonal plane surfaces of reference.