Background Living in a multicat household has been implicated as a risk factor for various feline issues, but evidence is often anecdotal or based on retrospective studies. Methods Data from the Bristol Cats Study, a UK longitudinal study of pet cats, were used. Cats were included if they had remained in either a single cat or multicat household between questionnaires 1 (two months old to four months old) and 5 (two-and-a-half years old). Univariable and multivariable logistic regression models were used to analyse associations between single cat/multicat households and measures of health and behaviour (overweight/obesity, abscesses/cat bites, negative interactions with owner and periuria). Multicat households were also subcategorised according to whether owners had reported agonistic behaviour between household cats. Results There was no evidence of association between household type and the likelihood of obesity, abscesses or periuria. The likelihood of negative interactions with the owner (eg, growling or hissing) was influenced by the cats’ relationships; cats in non-agonistic multicat households had decreased odds of negative interactions with the owner, compared with single and agonistic multicat households (P<0.001). Conclusion Living in a multicat households per se was not a risk factor for the health and behaviour issues investigated, but the intercat relationship is important.