The problem of control design for robotic arms manipulating unknown flexible payloads is considered in this paper. Control design based on neglecting the internal dynamics of the payload will result in degraded performance, increased task execution time, and even failure in performing tasks. At the same time, the characteristics of payloads to be handled vary with application. These considerations make it impractical to outfit the payload with sensors. A novel scheme utilizing a force torque sensor at the wrist of the manipulator is introduced in this paper. A controller utilizing the wrist torque feedback from the sensor is designed as a function of parameters of the payload dynamics. An adaptive scheme for online identification of these parameters and adaptation of controller parameters is discussed. The scheme is implemented on a single-link manipulator carrying a flexible unknown payload. Experimental results validate the fact that the adaptive control maintains a robust performance for high speed slewing and varying payloads.