Advanced language proficiency is a requirement for public service interpreting, and yet, research has not described this construct holistically in interpreting studies. Previous studies have suggested that public service interpreters primarily have a migration background, and asymmetrical language proficiency. The present study reports findings of these aspects from a questionnaire that was conducted to investigate the linguistic background of Spanish-Swedish public service interpreters in Sweden. A total of 118 Spanish-Swedish interpreters answered the questionnaire. Results show that the interpreters have asymmetrical language proficiency but do not primarily have a migration background. Moreover, it is indicated that asymmetrical language proficiency and migration background have an impact on the likelihood of public service interpreters being state authorized. However, there is a need for further research on these aspects to better understand details regarding both public service interpreters in Sweden and public service interpreters internationally.