Studies over the past two decades have provided relevant data on the relationship between music and reading abilities although they fundamentally refer to aspects of the first language reading process of young children. The foreign language reading acquisition process of adult learners has, in this sense, been less explored. Research in this area refers to working memory as a "common cognitive marker" for musical aptitude and reading ability, but little is known about the relationship between musical aptitude and silent reading fluency of adult foreign language learners, the hallmark of skilled readers. Specifically, this study seeks to determine whether musical aptitude as well as cognitive factors such as working memory, general intelligence and plurilingualism could contribute to the understanding of adults' silent reading abilities in a foreign language. For this purpose, thirty-eight undergraduates, native speakers of German and learners of Spanish, were tested. Additionally, their FL reading comprehension level and their musical training were controlled to categorise the learners. Our data shows a strong association of musical aptitude, working memory, general intelligence and plurilingualism with learners' foreign language silent reading fluency. In addition, a multiple linear regression analysis reveals that musical aptitude and knowledge of different foreign languages influence their silent reading fluency. But when in a second linear regression the lower reading proficiency level (A2) was introduced as a controlling variable, only musical aptitude is significant. In conclusion, further studies on the silent reading capacity of adult foreign language learners need to consider abilities such as musical aptitude and plurilingualism to better understand the whole reading acquisition process.