Background: The current study investigated the effects that vertical display oscillation had on the development of both vection and simulator sickness. Methods: Sixteen subjects were exposed to optic flow displays, which simulated either: (i) constant velocity forward self-motion (pure radial flow); or (ii) combined constant velocity forward and vertically oscillating self-motion (radial flow with vertical oscillation at one of three frequencies: 1.8, 3.7 or 7.4 Hz). During each 10-min display exposure, subjects rated the strength of their vection and 8 symptoms listed on the Subjective Symptoms of Motion Sickness (SSMS) scale at 2-min intervals. Subjects also completed the Simulator Sickness Questionnaire (SSQ) designed by Kennedy and colleagues before and after each trial, which generated a total SSQ score and three SSQ sub-scores (nausea, oculomotor symptoms, and disorientation). Results: Vertically oscillating displays (Mean = 5.51; S.D. = 2.5) were found to produce significantly stronger vection ratings than non-oscillating displays (Mean = 3.56; S.D. = 2.1). Vertically oscillating displays (Mean = 58.18; S.D. = 32.2) were also found to produce significantly more severe sickness (as rated by total SSQ scores) than non-oscillating displays (Mean = 29.67; S.D. = 24.7). Both vection and sickness symptoms increased in magnitude with prolonged exposure to optic flow. Conclusions: Our findings appear to represent a special case in visual self-motion perception, where high-frequency vertical oscillation both enhances vection and increases simulator sickness, when it is incorporated into an optic flow display simulating constant velocity self-motion in depth.