The paper addresses the output tracking of a class of uncertain nonlinear output feedback systems affected by disturbances that are known to be bounded but are otherwise unknown. The system uncertainty is parametrised by a parameter vector of which a normed upper bound is known. An adaptive controller is designed to guarantee arbitrary disturbance attenuation on the output tracking error for smooth reference signals under the minimum phase assumption. The paper represents an extension of disturbance decoupling results to uncertain systems as well as an extension of adaptive control results to the disturbance decoupling problem. © IEE, 1999.