In 'sympathetic horsemanship' the importance of the natural behaviour of the horse and the use of body language in communication is emphasised. However, it is unclear what effect sympathetic horsemanship has on the welfare of horses. During a 5-week starting period the effect of a sympathetic (ST) versus a conventional (CT) training method was studied using 28 young Warmblood horses. Behavioural observations during the starting period as well as during a standardised final riding test were performed by trained observers. A Wilcoxon matched-pair test was used to detect differences within groups, Mann-Whitney-U to test differences between groups, and principal component analysis (PCA) to evaluate the effect on multiple variables simultaneously. A human-approach test showed that ST horses snorted significantly less compared to CT horses (P=0.006) after the training period. Furthermore, CT horses showed more fear and stress-related behaviours during training such as 'body tension' (P<0.001), 'high head carriage' (P<0.001), 'lip movements' (P=0.008) and 'teeth grinding' (P=0.03). Principal component analysis demonstrated that horses showed consistent differences in a range of behavioural and heart-rate parameters between groups. Behavioural parameters and technical performance during the standardised final riding test did not differ significantly between groups, but mean heart rate was higher for CT horses (P<0.001). The results suggest that applying a sympathetic training method when starting young horses did not compromise technical performance, but seemed to reduce stress during training compared to a conventional training method.