Timely adoption is essential for shelters to prevent unnecessary illness or euthanasia in cats (Felis catus). Many studies have examined the role of individual cat characteristics and environmental factors in facilitating cat adoptions, but none have looked at the role the number of cats being adopted plays. In this study, we examined whether or not adopting cats in pairs influences adoption times, in addition to commonly studied factors. We then collected video data on a small subset of cats to determine whether pairs that were adopted together differed behaviourally from pairs who were not. Our results demonstrate that cats who are adopted as part of a multi-cat outcome spent three days (42%) longer on the adoption floor than those adopted individually, independently of other factors such as age and coat colour. This difference increased to 13 days (185%) longer if the cat had a notification indicating they must be adopted together with another cat. While behavioural data show that these pairs of cats engage in significantly more affiliative behaviour with each other than cats who were adopted singly, there was a large discrepancy between which pairs the shelter classified as multi-outcome and those who would be classified that way based on behaviour alone. We suggest that decisions to place cats together should be made carefully given the potential adverse impacts of keeping cats in the shelter longer. Further, we suggest that guidance should be developed to help shelters accurately and consistently identify which cats merit a multi-outcome adoption.