Motion sickness increases during exposure to low frequency motion, but there is little understanding of how sickness reduces after motion has ceased. The magnitude of lateral oscillation affects the incidence of motion sickness, but the relation between motion magnitude and motion sickness is not well established. It was hypothesised that motion sickness would increase with increasing magnitude of combined lateral and roll oscillation and also increase with increasing duration of exposure. In four separate sessions, 20 subjects were exposed to combined 0.1 Hz sinusoidal lateral oscillation with 50% roll compensation. Each session consisted of four successive periods of 15-minute motions presented without a break (total duration 1 hour). Each 15-minute motion was either a high magnitude motion (H) (±1.26 ms-2 lateral oscillation with ±3.66° roll oscillation) or a low magnitude motion (L) (±0.63 ms-2 lateral oscillation with ±1.83° roll oscillation). The four conditions were: (i) LLLL, (ii) HHHH, (iii) LHHL, (iv) HLHL. Subjects gave ratings of their symptoms every minute for 80 minutes (from 5 minutes before the start of the motion until 15 minutes after the motion had ceased) using a seven-point illness rating scale. Subjects were seated in a closed cabin on a seat with a high backrest and were exposed to the four conditions at 1-week intervals. The high magnitude motion caused more sickness than the low magnitude motion. Sickness ratings decreased during periods of low magnitude motion and after the cessation of motion.