Objectives: Research suggests Animal Assisted Interventions (AAI) reduce negative outcomes in medical settings, but quantitative examinations of their effects on medical outcomes such as pain, anxiety, and distress are lacking. Design: A comprehensive literature search and meta-analysis were conducted in which 22 studies (13 child, 9 adult) met inclusion criteria. Both intervention versus control and intervention pre-post effect sizes were computed using a random effects model. Results: The overall intervention versus control effect size was large and significant (d = 1.65, 95% CI = 0.46-2.832). Similarly, the pre-post effect size was large and significant (d = 2.19, 95% CI = 0.74-3.64). Conclusions: The results of this meta-analysis indicate that AAI can yield large effects across a number of medically relevant outcomes. There is, however, substantial methodological variation across studies and more randomized clinical trials with stronger methodological controls are needed to establish the effectiveness of AAI compared to other interventions.