The relationship between perfectionism – perfectionistic strivings and perfectionistic concerns – and athletic performance is contested and inconsistent. The present study explored the possibility that one explanation for this inconsistency is the assumption that the relationship is linear. In two samples, we tested alternative non-linear relationships between perfectionism and real-world competitive athletic performance. Sample one comprised 165 Swedish track and field athletes (57 % competing in female category, 42 % in male category; Mage = 16.93 years) and sample two comprised 157 British track and field athletes (55 % competing in female category, 43 % in male category; Mage = 18.42 years). Testing for linear and non-linear relationships, we found a quadratic effect whereby higher perfectionistic strivings had both positive increasing (i.e., U-shape; sample 1) and positive decreasing (i.e., inverted U-shape; sample 2) relationships with performance. We conclude that there may be circumstances when perfectionistic strivings contribute to better and worse sport performance, and that this relationship can be curvilinear.