Introduction: Icelandic horse competitions are popular in Scandinavia, yet understanding the rider-horse interaction in the tölt gait is currently limited. It is known that a heavier rider leads to shorter and more frequent steps during tölt.1 Also, an imbalanced rider can result in overextension in the horses’ limbs, which can cause lameness.2 Therefore, understanding the effects of rider asymmetry (i.e.,being unable to stay balanced) is important for both performance and horse welfare. Aim: The aim of this study was to identify whether rider asymmetry affects tölt performance in Icelandic horses. Method: Two different horses were ridden in tölt by four riders on separate occasions. Riders were equipped with Pedar foot pressureinsoles (Novel Electronics, Germany) to measure rider balance and a 3D motion-analysis system (Noraxon, Arizona, USA) to examine movement around the pelvisin both left and right rein directions. Lateral Advanced Placement (LAP)3 was used to determine tölt performance and was calculated from visual inspection of 60 Hzvideo footage. Paired samples t-tests were used to determine differences in LAP, lateral pelvic movement, and foot pressure between left and right rein. Results are expressed as mean±SD Results: LAP was significantly greater for left compared with right rein (23±1% vs. 21±0%; p = 0.002) and riders had significantly more lateral pelvic movement for right compared with left rein (2.6±0.5° vs. 1.5±0.5°;p=0.002). However, there was no foot pressure asymmetry for left vs. right rein(12±6 N vs. 10±6 N; p=0.670). Conclusions: Riders perform better in tölt on left rein and lateral pelvic movement appears to influence tölt quality. Coaches should focus on instructing riders to balance their seat to improve performance and equine welfare.