The Theme of Sirmium () was a Byzantine administrative unit (theme), which existed in present-day Serbia, Croatia and Bosnia and Herzegovina in the 11th century.
ðə θˈiːm ʌv sˈɜːmiəm wʌzɐ bˈɪzɐntˌiːn ɐdmˈɪnɪstɹˌeɪɾɪv jˈuːnɪt θˈiːm, wˌɪtʃ ɛɡzˈɪstᵻd ɪn pɹˈɛzəntdˈeɪ sˈɜːbiə, kɹoʊˈeɪʃə ænd bˈɑːsniə ænd hˈɜːzɪɡˌɑːvɪnə ɪnðɪ ɪlˈɛvənθ sˈɛntʃɚɹi.