Optic flow in visual displays or virtual environments often induces motion sickness (MS). We conducted two studies to analyze the effects of stereopsis, background sound, and realism (video vs. simulation) on the severity of MS and related feelings of immersion and vection. In Experiment 1, 79 participants watched either a 15-min-long video clip taken during a real roller coaster ride, or a precise simulation of the same ride. Additionally, half of the participants watched the movie in 2D, and the other half in 3D. MS was measured using the Simulator Sickness Questionnaire (SSQ) and the Fast Motion Sickness Scale (FMS). Results showed a significant interaction for both variables, indicating highest sickness scores for the real roller coaster video presented in 3D, while all other videos provoked less MS and did not differ among one another. In Experiment 2, 69 subjects were exposed to a video captured during a bicycle ride. Viewing mode (3D vs. 2D) and sound (on vs. off) were varied between subjects. Response measures were the same as in Experiment 1. Results showed a significant effect of stereopsis; MS was more severe for 3D presentation. Sound did not have a significant effect. Taken together, stereoscopic viewing played a crucial role in MS in both experiments. Our findings imply that stereoscopic videos can amplify visual discomfort and should be handled with care.