Purpose: The purpose of this study was to evaluate the impact of code-switching on Spanish/English bilingual listeners' speech recognition of English and Spanish words in the presence of competing speech-shaped noise. Method: Participants were Spanish/English bilingual adults (N = 27) who were highly proficient in both languages. Target stimuli were English and Spanish words presented in speech-shaped noise at a -14-dB signal-to-noise ratio. There were 4 target conditions: (a) English only, (b) Spanish only, (c) mixed English, and (d) mixed Spanish. In the mixed-English condition, 75% of the words were in English, whereas 25% of the words were in Spanish. The percentages were reversed in the mixed-Spanish condition. Results: Accuracy was poorer for the majority (75%) and minority (25%) languages in both mixed-language conditions compared with the corresponding single-language conditions. Results of a follow-up experiment suggest that this finding cannot be explained in terms of an increase in the number of possible response alternatives for each picture in the mixed-language condition relative to the single-language condition. Conclusions: Results suggest a cost of language mixing on speech perception when bilingual listeners alternate between languages in noisy environments. In addition, the cost of code-switching on speech recognition in noise was similar for both languages in this group of highly proficient Spanish/English bilingual speakers. Differences in response-set size could not account for the poorer results in the mixed-language conditions.