Perfectionistic athletes may train harder and for longer than non-perfectionistic athletes, leaving them susceptible to elevated levels of training distress. So far, however, no study has investigated the relationships between perfectionism and training distress, a key indicator of overtraining syndrome. Furthermore, no study has determined psychological predictors of overtraining syndrome. Using a two-wave design, the present study examined perfectionistic strivings, perfectionistic concerns, and training distress in 141 junior athletes (mean age 17.3 years, range 16-19 years) over 3 months of active training. Multiple regression analyses were employed to test cross-sectional and longitudinal relationships between perfectionism and training distress. In all analyses, perfectionism emerged as a significant predictor, but strivings and concerns showed differential relationships. When the cross-sectional relationships were regarded, perfectionistic concerns positively predicted training distress (p < .01), whereas perfectionistic strivings negatively predicted training distress (p < .001). When the longitudinal relationships were regarded, only perfectionistic concerns predicted increases in training distress (p < .05), whereas perfectionistic strivings did not (p > .05). The findings suggest that sports scientists who wish to identify athletes at risk of overtraining syndrome may monitor athletes' perfectionistic concerns as a possible risk factor.