Given the requirement of professional jockeys to make-weight daily, we tested the hypothesis that Flat and National Hunt (Jump) jockeys would display compromised health markers (bone health, vitamin D, liver and kidney function and mood) compared with established clinical norms, with Flat jockeys affected the greater. Daily energy intake was lower in Flat compared with Jump jockeys (6.11±1.25 vs. 7.47±0.83 MJ.day, P=0.01) whereas there was no difference in urine osmolality (811±198 vs. 678±317 mOsmol.kg respectively, P=0.13). Serum total 25(OH)D was insufficient in Flat and Jump jockeys (37.6±28 vs. 35.1±14 nmol.L) respectively although there was no difference between groups (P=0.79). Markers of bone metabolism (Plasma ß-carboxy-terminal cross-linked teleopeptide (CTX) and Intact Parathyroid Hormone (PTH) and liver and kidney function were within clinical normative ranges although CTX and PTH were higher than average. Abnormal mood profiles were observed in both groups although significantly poorer in the Flat jockeys (P=0.01). We conclude that the current practices of jockeys to make-weight may have detrimental effects upon their health with Flat jockeys affected more so than Jump jockeys. Future studies should investigate the effects of improved dietary practices on the mental and physical health of Flat and Jump jockeys. © Georg Thieme Verlag KG Stuttgart · New York.