In recent years, there has been a growing research interest in the analysis of errors adults make while learning a second language. The underlying objective of most of these analyses has been to reveal the systematicity of adult errors in an effort to understand the process of adult second language learning. This paper deals with errors from a different point of view, namely, from the listener or reader's point of view. The question asked is, which types of errors cause the listener or reader to misunderstand the message intended by the EFL learner? Based on the judgments of native English speakers about the comprehensibility of hundreds of sentences containing errors of EFL learners all over the world, linguistic criteria for determining the communicative importance of learners' errors are suggested. Areas of English syntax that cause important communicative errors usually neglected in most EFL training materials are discussed. The paper concludes with the application of this particular error analysis approach to the EFL classroom. (Author)