This study examined factors related to reading comprehension in adolescents who spoke English as a first language (L1) and English as a second language (L2). Measures of decoding, vocabulary knowledge, and reading comprehension were administered to 31 L1 and 44 L2 speakers. English L2 adolescents scored significantly lower than their L1 peers on all measures. Factor analyses produced different configurations of variables for each group. For L1 learners, measures of decoding and vocabulary were separate factors but were one factor for English L2 learners. For the L1 learners, it was only the measure of vocabulary that was a significant predictor of reading comprehension. For L2 learners, decoding, vocabulary, and the interaction of decoding and vocabulary were all significant predictors of reading comprehension. Relations among these variables in adolescents who are beginning to learn English as an L2 are explored. (Contains 6 tables.)