OBJECTIVE: Previous studies have reported that brain-injured patients frequently suffer from cognitive impairments such as attention and concentration deficits. Numerous rehabilitation clinics offer animal-assisted therapy (AAT) to address these difficulties. The authors' aim was to investigate the immediate effects of AAT on the concentration and attention span of brain-injured patients. METHOD: Nineteen patients with acquired brain injury were included in a randomized, controlled, within-subject trial. The patients alternately received 12 standard therapy sessions (speech therapy, physiotherapy, occupational therapy) and 12 paralleled AAT sessions with comparable content. A total of 429 therapy sessions was analyzed consisting of 214 AAT and 215 control sessions. Attention span and instances of distraction were assessed via video coding in Noldus Observer. The Mehrdimensionaler Befindlichkeitsbogen ([Multidimensional Affect Rating Scale] MDBF questionnaire; Steyer, Schwenkmezger, Notz, & Eid, 1997) was used to measure the patient's self-rated alertness. Concentration was assessed through Visual Analogue Scale (VAS) via self-assessment and therapist's ratings. RESULTS: The patients' attention span did not differ whether an animal was present or not. However, patients displayed more instances of distraction during AAT. Moreover, patients rated themselves more concentrated and alert during AAT sessions. Further, therapists' evaluation of patients' concentration indicated that patients were more concentrated in AAT compared with the control condition. CONCLUSIONS: Although the patients displayed more instances of distraction while in the presence of an animal, it did not have a negative impact on their attention span. In addition, patients reported to be more alert and concentrated when an animal was present. Future studies should examine other attentional processes such as divided attention and include neurobiological correlates of attention. (PsycINFO Database Record