BACKGROUND: Space motion sickness (SMS) remains a troublesome problem during spaceflight. The subjective vertical (SV) conflict theory postulates that all motion sickness provoking situations are characterized by a condition in which the SV sensed from gravity and visual and idiotropic cues differs from the expected vertical. This theory has been successfully used to predict motion sickness in different vehicles on Earth.METHOD: We have summarized the most outstanding and recent studies on the illusions and characteristics associated with spatial disorientation and SMS during weightlessness, such as cognitive map and mental rotation, the visual reorientation and inversion illusions, and orientation preferences between visual scenes and the internal z-axis of the body.RESULTS: The relationships between the SV and the incidence of and susceptibility to SMS as well as spatial disorientation were addressed.CONCLUSION: A consistent framework was presented to understand and explain SMS characteristics in more detail on the basis of the SV conflict theory, which is expected to be more advantageous in SMS prediction, prevention, and training.Chen W, Chao J-G, Wang J-K, Chen X-W, Tan C. Subjective vertical conflict theory and space motion sickness. Aerosp Med Hum Perform. 2016; 87(2):128–136.