The aim of this randomized controlled trial was to investigate the effect of a 4- to 6-week multimodal program of exercise, relaxation and psychoeducation on physical capacity, functional performance and quality of life (QOL) in allogeneic hematopoietic cell transplantation (allo-HSCT) adult recipients. In all, 42 patients were randomized to a supervised multimodal intervention or to a control group receiving usual care. The primary end point was on aerobic capacity measured in VO(2) max. Secondary end points were muscle strength, functional performance, physical activity level, QOL, fatigue, psychological well-being and clinical outcomes. The multimodal intervention had a significant effect on physical capacity: VO(2) max (P<0.0001) and muscle strength: chest press (P<0.0001), leg extension (P=0.0003), right elbow flexor (P=0.0009), right knee extensor (P<0.0001) and functional performance (stair test) (0.0008). Moreover, the intervention group showed significantly better results for the severity of diarrhea (P=0.014) and fewer days of total parenteral nutrition (P=0.019). Longitudinal changes in QOL, fatigue and psychological well-being favored the intervention group, but did not reach statistical significance. Assignment of a multimodal intervention during allo-HSCT did not cause untoward events, sustained aerobic capacity and muscle strength and reduced loss of functional performance during hospitalization.