Bilingualism, or the use of two languages by one person (Mackey, 2000), has become a rule rather than an exception in the contemporary society. Similarly, code-switching, that is, alternating between two languages during a single conversation (Gardner-Chloros, 2009), has been observed and described in almost every corner of the world. The aim of this study was to investigate code-switching habits of Croatian teenage learners of English. The study was conducted on a sample of 59 Croatian high school students who had been learning English as a foreign language in Zagreb. The participants’ code-switching practices were examined using a questionnaire. All the participants reported being exposed to English outside of school on a daily basis. The results of the study showed that teenagers code-switched between Croatian and English in informal conversations with their friends and peers and that they refrained from such language behavior when communicating with older generations or people who did not have a high level of proficiency in English. Furthermore, the results showed that the main reason why teenagers engaged in code-switching was a lack of appropriate words and phrases in Croatian to express their ideas and opinions. Finally, it was confirmed that high school students used English words and phrases more often than whole English sentences. The overall results of the study suggest that English is becoming an important means for Croatian teenagers who use it to fulfil their communicative needs when interacting with one another despite their shared first language.