A new output feedback variable structure model reference adaptive control (VS-MRAC) scheme is proposed in this paper for uncertain plants with relative degree one. The scheme is based on the existing VS-MRAC structure together with a high gain switching mechanism to adjust the variable structure control signal. The main features of the scheme are that (1) the pre-specified transient and steady-state performance specifications for tracking error can be guaranteed, (2) it does not require the plant high frequency gain sign to be known a priori, (3) the usual assumption for MRAC system that the reference model is strictly positive real (SPR) is not needed and (4) the plant input disturbance, which is assumed to be unknown but bounded, can be completely rejected. (c) 2006 Elsevier Ltd. All rights reserved.