We investigated the accuracy of audio-visual simultaneity judgments in a rapid serial visual presentation (RSVP) task. Eleven healthy participants indicated which RSVP stimulus was presented simultaneously with a tone. Results showed that on average in 33% of all trials the simultaneously presented letter was correctly identified. As compared to that, the letters preceding or following the tone were respectively identified in about 20% of the trials, and the letters presented two lags before or after the tone in about 6% of the trials. This pattern of results was consistent across subjects (F=13.85, p<0.05). We furthermore tested whether the accuracy of the simultaneity judgment was related to the number of RSVP stimuli preceding the tone, reflecting the recently described ‘attentional awakening’ effect (Ariga & Yokosawa (2008), Psychol Res, 72(2), 192-202) in RSVP. No significant difference in the accuracy of simultaneity judgments in dependence of the number of RSVP stimuli was observed.