Human-animal research into the benefits of pet keeping is growing, yet very little research has considered welfare implications of keeping particularly pet types. Animal welfare issues raised regarding keeping non-human primates as pets has recently led to a parliamentary debate in the UK about the legality of owning such animals. Concerns for such animals are due to the wide range of problems associated with keeping wild animals as human companions. This study aimed to investigate psychological and behavioural effects of being kept as pets on capuchins (Cebus spp.), a popular primate pet.
We did this in two ways: firstly, by investigating evidence for psychological disorders in a population of 19 ex-pet capuchins, and secondly by comparing the frequencies of stress–related behaviours and stereotypies between these ex-pets and zoo-living animals of the same genus. All of the ex-pet capuchins had a history of stressful life events, and all were non-maternally reared. To explore psychological disorders, we developed for use by keepers of capuchins a questionnaire based on the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) criteria for three human psychological disorders: post-traumatic stress disorder, generalised anxiety disorder and major depression.
Behavioural data revealed that ex-pet capuchins displayed higher rates of self-directed (p>.005) and stereotypic behaviours (p>.005) than zoo-living capuchins, and also spent less time grooming (p<.005), a key primate social behaviour. Five of the ex-pets met the full criteria of a psychopathological condition in the past, and two continued to do so at the time of the study.
 Our findings provide evidence that for capuchins, being kept as pets leads to the development of serious enduring psychopathology and associated behavioural problems. the negative impacts on the psychological wellbeing of capuchin monkeys demonstrated here, observed years after their time as pets, highlight the questionable ethics of pet ownership of non-human primates, even though this practice is not currently illegal in the UK.