Background and research question Reading comprehension in one’s first language is a broadly researched phenomenon. However, technological, social and economic changes have led to an increase of people learning to read in a foreign language (Saiegh-Hadad & Geva, 2010; Bernhardt, 2011). Thus, there is an increasing interest in research about second language reading. Reading in the second language is similar to, but at the same time, different in many ways than reading in the first language (Jiang, 2011; Yamashita & Shiotsu, 2017). It is important to understand which skills play a significant role in the development of second language reading. It is well established by existing research that second language vocabulary knowledge and first language reading ability are important components of second language reading comprehension (Raudszus et al., 2018; Raudszus et al., 2019; Jeon & Yamashita, 2014; Yamashita & Shiotsu, 2017; O’Connor et al., 2019; Schaars et al., 2019; Verhoeven, Voeten & Vermeer, 2019; Brevik et al., 2016). Furthermore, cross-linguistic transfer of skills has been strongly suggested between the first and the second language (Verhoeven, Perfetti & Pugh, 2019). Some theories have been suggested about the interaction and the transfer between the two languages (Cummins, 1979; Clarke, 1978; Bernhardt, 2011). However, there is not yet an agreement about how and when this transfer occurs. Moreover, there is lack of studies on the transfer of knowledge between the two languages with variation in the language background (Raudszus et al., 2018; Park, 2013). This study’s purpose is to investigate the relationship between second language reading comprehension, second language vocabulary knowledge and first language reading comprehension with Norwegian as the first and English as the second language. It is also desired to see whether there is linguistic transfer of knowledge between Norwegian and English. The study is based on the following research question: To what extent does L2 (English) vocabulary account for L2 reading comprehension, after accounting for L1 (Norwegian) reading comprehension, in adult native Norwegian speakers? Method The study is based on data collected for the Norwegian part of an international study named Multilingual Eye-Tracking Corpus (MECO) (Cop et al., 2017) about eye-movements of adults during reading in many languages with different writing systems. The sample consists of 50 young adults with Norwegian as their first language. A quantitative approach has been used and the participants have been tested with various psychometric tests. The study is non-experimental and no variables were manipulated. Multiple hierarchical regression analysis has been used to investigate to what extend first language reading comprehension and second language vocabulary knowledge can predict second language reading comprehension in adult native Norwegian speakers. In addition, bivariate correlation analysis has been conducted to investigate the relationship between these variables. Results In line with previous research, the correlation analysis showed that both first language reading comprehension and second language vocabulary knowledge correlate strongly with second language reading comprehension. The hierarchical regression analysis showed that first language reading comprehension and second language vocabulary accounted for the half of second language reading comprehension’s variance. This finding is in line with the existing theory about cross-linguistic transfer and the factors that influences it.