BACKGROUND: Previous studies on nitrogen narcosis have focused on how it affects behavior, performance, and cognitive function. However, little is known about the effects of nitrogen narcosis on the emotional processing of external stimuli. METHOD: We presented 20 volunteers with images from the International Affective Picture System (IAPS) and categorized as unpleasant, neutral, or pleasant, while sitting in a hyperbaric chamber at the surface (101,3kPa) and at 39 m equivalent depth (496.4 kPa). The participants rated the images along three affective dimensions: valence (intrinsic attractiveness or aversiveness of a stimuli), arousal, and dominance. RESULTS: In the valence dimension there was no significant effect of increased pressure or interaction between increased pressure and image category. There was a significant interaction between image category and the pressure at which the images were viewed in the arousal dimension. The mean arousal rating score for unpleasant stimuli was 0.5 point (on a 9-point scale) lower at hyperbaric conditions and equal arousal rating score for neutral stimuli in general. DISCUSSION: The absence of any effect of pressure in the valence dimension suggests that divers have no impairment in their ability to determine the pleasantness or unpleasantness of different stimuli. Furthermore, this study suggests that the effects of nitrogen narcosis on the emotional processing of external stimuli are primarily evident in the arousal dimension. Although differences in arousal ratings were relatively small in magnitude, even a small alteration in emotional response to external stimuli might be important in the context of deep diving.