OBJECTIVES: Over the last three decades, animal assisted therapy (AAT) has been proposed as an add-on treatment to concomitant pharmacotherapy/psychotherapy for the management of several mental health and neurological disorders. The benefits of AAT have been observed across a range of indications including patients with dementia, schizophrenia, and autism. The current systematic review (SR) was conducted to evaluate the use of AAT in patients with depression and/or anxiety. METHODS: A search was conducted in MEDLINE, EMBASE and the Cochrane Library. Eligible studies included those enrolling patients with depression and/or anxiety at baseline who underwent AAT of any form and reported outcome on symptoms of depression and/or anxiety, particularly response or remission. RESULTS: Of the 937 publications screened, 12 met the inclusion criteria (5 randomised controlled trials [RCTs] and 7 observational studies). Various animals were employed as part of the AAT regimen, including dogs (7/12 studies); dogs and cats (1/12); horses (1/12); dolphins (1/12); and farm animals (such as cows, pigs and chickens [2/12]). Across the included studies, enrolled patient numbers ranged from 12 to 80 and study follow up from 15 minutes to 12 weeks. Four studies reported changes in symptoms of depression, five reported changes in depression and anxiety symptoms and three reported changes in anxiety symptoms. All studies reported an improvement in depression and/or anxiety symptoms following AAT. An improvement in symptoms of depression was reported in 8/9 studies (including 4 RCTs), reaching statistical significance in six studies. An improvement in symptoms of anxiety was reported in 8/8 studies (including 4 RCTs), reaching significance in four studies. CONCLUSIONS: This SR provides evidence that AAT can be beneficial as an additional therapy in the treatment of depression and/or anxiety disorders. Further comparative evidence and data from larger cohort studies with sufficient follow up are required to confirm these findings.