In this paper, a robust model reference adaptive control of a cantilevered flexible structure with unknown spatiotemporally varying coefficients and disturbance is investigated. Any mechanically flexible manipulators/structures are inherently distributed parameter systems whose dynamics are described by partial, rather than ordinary, differential equations. Robust adaptive control laws are derived by the Lyapunov redesign method on an infinite dimensional Hilbert space. Under the assumption that disturbances are uniformly bounded, the proposed robust adaptive scheme guarantees the boundedness of all signals in the closed loop system and the convergence of the state error near to zero. With an additional persistence of excitation condition, the parameter estimation errors are shown to converge near to zero as well.