The purpose of this study was to evaluate an individualized hydration intervention, and its effects on an elite wheelchair marathon racer’s body mass, diuresis, and hydration status at ~4000 m altitude. Total daily fluid intake, urine excretion, fluid intake during training sessions (Fluid), and urine specific gravity upon wakening (SG AM) and before bedtime (SG PM) were assessed before, during the course, and after a 5-wk training camp at 3860-4090 m altitude. Body mass and total sodium daily intake (Na⁺) were recorded. Increased fluid requirements (Cohen´s d = 1.21) and diuresis (Cohen´s d ≥ 2.85) were observed in a wheelchair athlete at altitude. Interestingly, hydric balance (HB) was not ideal (± 2 %) when following hydration rates suggested for able-bodied athletes.