The study examined whether individual differences in high school first language (L1) reading achievement and print exposure would account for unique variance in second language (L2) written (word decoding, spelling, writing, reading comprehension) and oral (listening/speaking) proficiency after adjusting for the effects of early L1 literacy and verbal skills, cognitive ability in L1, and L2 aptitude. Participants were administered measures of L1 word decoding, spelling, reading comprehension, phonological awareness, receptive vocabulary, listening comprehension, and cognitive ability in 1st through 5th grades; L2 aptitude in 9th grade; and L1 reading achievement, L1 print exposure, and L2 proficiency in 10th grade. The findings showed that L1 reading achievement in 10th grade made significant and unique contributions to L2 word decoding, L2 reading comprehension, L2 listening/speaking, and overall L2 proficiency after adjusting for the effects of L1 literacy and verbal skills, cognitive ability in L1, and L2 aptitude. Subsequent analyses showed that L1 print exposure variables made unique contributions to L2 reading comprehension, L2 decoding, L2 writing, L2 listening/speaking, and overall L2 proficiency even after adjusting for the effects of L1 literacy and verbal skills during elementary school, cognitive ability in L1, L2 aptitude, and 10th-grade reading achievement. The results suggest that stronger L1 reading skills are related to stronger L2 outcomes and that opportunity for and engagement in L1 literacy experiences may also be related to differences in L2 proficiency.