The aim of this study is to investigate what differences there are in vocabulary comprehension between pupils with Swedish as a first and second language. The strategies used for understanding unknown words are also investigated. Above all, the aim of this study is to see whether the subject teacher is aware of which words could be difficult to understand for pupils with Swedish as a second language and if she is aware of their vocabulary ability.          Both quantitative and qualitative methods were used in the form of observation, vocabulary test and semi-structured interviews with both pupils and subject teacher. There were 12 informants from a national gymnasium programme participating in the vocabulary test. Seven of them had Swedish as a second language and six of them has Swedish as a first language. Six informants participated in interviews.          The results showed that there were both quantitative and qualitative differences between the groups. The results also imply that informants with higher scores in the vocabulary test are more aware of which methods to use in the hearing and reading of an unknown vocabulary. The subject teacher was well aware of which words in teaching could be hard to understand for second language pupils, but underestimated the pupils’ knowledge of words.          The test results were not statistically tested and could therefore not be generalized for the population. Contemporary field research supports the test results.