A 10-month prospective study was carried out which examined changes in behaviour and health status in 71 adult subjects following the acquisition of a new pet (either dogs or cats). A group of 26 subjects without pets served as a comparison over the same period. Both pet-owning groups reported a highly significant reduction in minor health problems during the first month following pet acquisition, and this effect was sustained in dog owners through to 10 months. The pet-acquiring groups also showed improvements in their scores on the 30-item General Health Questionnaire over the first 6 months and, in dog owners, this improvement was maintained until 10 months. In addition, dog owners took considerably more physical exercise while walking their dogs than the other two groups, and this effect continued throughout the period of study. The group without pets exhibited no statistically significant changes in health or behaviour, apart from a small increase in recreational walking. The results provide evidence that pet acquisition may have positive effects on human health and behaviour, and that in some cases these effects are relatively long term.