Introduction. Relative Energy Deficiency in Sport (RED-S) has many known negative consequences on health and performance parameters. However, less is clear about the impact on performance in men, especially when athletes do not exhibit clear symptoms of RED-S like serious eating disorder or low bone mineral density with recurring stress fractures. In addition, there is still no available questionnaire for easy detection of RED-S in men. Aim of Study. To determine if a greater risk for RED-S, assessed by a short questionnaire, impacts cycling performance. Material and Methods. Young competitive male road cyclists (n = 47, age 14-22) completed the questionnaire, body composition analysis with bioelectrical impedance and incremental testing (measuring VO2max, peak power, relative peak power per kg and body fat percentage).These results were expressed relative to the results of cyclists competing at the same age and performing incremental testing in our laboratory (n = 580). In the questionnaire, we assessed number of sick days and injury-related days-of-training and a significant loss of body mass in the last month (>5%). If they had a significant weight loss or number of missed training days in the upper quartile, their risk for RED-S was recognized as increased. Results. 21 of 47 cyclists had an increased risk for RED-S that affected relative peak power (p = 0.008). We found no effect on VO2max, absolute peak power, and body fat percentage. Conclusions. An increased risk for RED-S as assessed with a short questionnaire affects relative peak power compared to relative peak power in competitive cyclists of the same age. This is a crucial parameter in cycling performance. A high number of cyclists with an increased risk (44.7%) is in agreement with studies suggesting the prevalence of RED-S in competitive cycling is high