Previously published studies report an improvement in hyperactivity following exposure to vestibular semicircular canal stimulation under eyes-open, lights-on conditions (conditions that provide visual feedback). To separate the effectiveness of vestibular stimulation from that of visual stimulation, 30 primary school children who met the criteria for having attention deficit disorder with hyperactivity were enrolled in a split-sample Latin square crossover study. The effects of just vestibular stimulation and of just visual stimulation were compared with the effect of combined vestibular and visual stimulation. Behavior ratings showed significant improvement at the end of the last treatment and at follow-up one year later; this is not easily explained by statistical regression, history, or the placebo effect. The most improvement was with solitary vestibular stimulation, which showed large effect sizes; however, differences from the other two conditions failed to reach significance at traditional p levels.