To make sound science-related decisions in a global society, individuals must possess a science identity, or see themselves as capable of doing and understanding science. Science identity development begins in school-aged years, when multilingual students (MLs) are often marginalised in the classroom due to language challenges and low expectations placed on them. This descriptive multiple case study explores the science identities expressed by six US high school MLs in their biology classrooms. Data from semi structured interviews were analysed through qualitative coding methods. Secondary data sources included field notes from observations conducted in each student's classroom six times during the school year. Results revealed that all MLs expressed science identity indicators, including feeling like a scientist, having a personal interest in science, and seeing science as related to their worlds. Other important identity indicators were not expressed among all students, such as views of themselves as 'good' science students, doing or using science outside of school, and career aspirations. Over half of MLs cited language as a direct barrier to their science identities. The study makes several contributions to the field of science education, which are detailed. Implications are presented for nurturing MLs' science identities in the formal classroom.