An animal’s welfare is directly impacted by its mental state, shaped by individual interpretations of experiences within an environment over a lifetime. For zoo-housed animals, visitors to the zoo are a fluctuating variable within that environment. To examine the impact of zoo visitors on five species of zoo-housed primates, this study uses each animal’s location within its habitat as an indication of internal mental state. Distance from visitor viewing glass is considered an indication of comfortability in the presence of visitors, and analysis considers primate-visitor proximity across increasingly large groups of zoo visitors. Analyses reveal a statistically significant but insubstantial decrease in primate distance from visitor viewing glass when visitors are present at each primate habitat, even as the number of visitors increases. This is thought to indicate no decrease in welfare due to the presence of zoo visitors.