Although the super-elevation and vehicle tilt mechanism of railway systems are intended to compensate for stationary lateral acceleration, this compensation can produce low-frequency vertical acceleration and roll motion. It is said that these vibrational factors tend to cause motion sickness. However, clear evidence that these vibration are the cause of motion sickness is not obtained. From medical, psychological and technological viewpoints, we summarize the points under discussion on the evaluation of motion sickness and outline future prospects of this study. Major topics are indices of motion sickness, international standard on evaluation method of motion sickness, cumulative effects of vibration and the characteristics of tilt sickness.