This study investigates whether there is a correlation between vocabulary proficiency in English and vocabulary proficiency in Swedish among newly arrived upper secondary students in Sweden. The focus lies here on the students’ passive vocabulary. The methods being used in this study are a vocabulary test investigating the students’ vocabulary proficiency in English and Swedish as well as a survey determining the students’ personal and educational background. Due to issues of validity and reliability, the findings of this study are not conclusive. Nevertheless, this study indicates that there is reason to believe that acquiring two second languages simultaneously at upper secondary school level can be challenging for newly arrived students which opens up for further research into that matter.