The purpose of the present cross-sectional, convenience sampled study was to ascertain differences in diet and lifestyle between cat (n 155) and dog (n 318) owners and their pets. Average cat ownership was 6.1 (SD 5) years and average cat's age was 6.9 (SD 5) years. Cats were reported to be overweight (14 %), fed ad libitum (87 %), given medication (11 %) and had health conditions (24 %). Cat's age was significantly and positively related to cat's weight, duration of illness, owner's BMI and some owners' dietary characteristics. Overweight in cats was significantly associated with overweight in older owners ( ≥ 60 years). Younger cat owners ( < 60 years) showed non-statistically significant trends between the owner's BMI and cat's overweight. Cat's age was inversely correlated with cat's and owner's activity levels. Dogs were owned for 5.5 (SD 4) years and mean dog's age was 5.9 (SD 4) years. Dogs were reported to be overweight (18 %), fed ad libitum (49 %), given medication (31 %) and had health conditions (34 %). Dog's age was positively associated with duration of illness. Dog's age was inversely correlated with amount of food fed, dog's activity and owner's exercise and intake of fruit, vegetables and whole grains. Dog's age was positively correlated with the owner's BMI and frequency of added fat consumption. Overweight in dogs was associated with overweight in older owners ( ≥ 60 years) and was correlated with poorer health in both the dog and the owner. Younger dog owners were more likely to have an overweight dog if they themselves were obese. Similarities were found in owner's and pet's diet and lifestyle issues with ageing. Overweight was associated with ageing, dietary, lifestyle and health issues in this sample. Older owners who were overweight had overweight pets. Strategies should be targeted towards decreasing both owner's and pet's overweight. The use of exercise and dietary interventions should be encouraged.