This article contributes to the field of reading assessment in English as a second language (L2). Few reading studies have been carried out at the upper secondary school level, and the present study provides insight into upper secondary school students' L2 reading proficiency. It examines whether such proficiency can be explained by reading proficiency in Norwegian as their first language (L1). The analysis uses data from two national reading tests, comprising a large sample of 16-year-old students (N = 10,331), and it is the first time reading across these languages has been investigated at this level. The results show a significant and meaningful relationship between students' reading proficiency in the two languages. The results also reveal marked reading differences in reading proficiency in the two languages among poor readers.