The emotional Stroop task is an experimental paradigm to study how emotional stimuli affect attention. Human participants typically need to categorize the color of a word or of a frame around an image. Latencies to identify the color are typically slowed down when the emotional valence of the word or image is negative rather than neutral (emotional Stroop effect). Here we investigated whether a similar effect could be found in chimpanzees. Six chimpanzees were trained on a touch screen task to choose, based on color, between two simultaneously presented stimuli. The stimuli on each trial were differently colored frames that contained identical images. After a training phase subjects were presented with four different categories of novel images: three categories of photographs of humans whose relationship with the subject differed across categories (veterinarian, stranger, caretaker), and control stimuli showing merely a white square. Because visits by the veterinarian are stressful to most subjects, we expected subjects to select the correct color less accurately and more slowly when the embedded picture depicted the zoo veterinarian than with any other stimulus category. For the first session, we found color selection to be indeed slower for trials presenting the veterinarian. Moreover, this effect was more pronounced for subjects whose last anaesthetization experience was more recent, indicating that emotional valence associated with the stimuli caused the slowdown. We propose our modified emotional Stroop task as a simple method to explore how emotional stimuli affect cognitive performance in nonhuman primates.