In this paper, we present an analytical method for estimating the bit error probability performance of a quadrature amplitude modulation (QAM) transmission system in the presence of impulse noise. Numerical results are demonstrated using parameters that are typical of the recently proposed Asymmetrical Digital Subscriber Lines ( ADSL) for digital transmission over the local copper telephone loop plant. It is shown that impulse noise can impact significantly on the performance of QAM system, such as the QAM-based ADSL, when operated on local telephone loops.