Objectives: To determine if providing informal care to a co-resident with dementia symptoms places an additional risk on the likelihood of poor mental health or mortality compared with co-resident non-caregivers.; Design: A quasi-experimental design of caregiving and non-caregiving co-residents of individuals with dementia symptoms provides a natural comparator for the additive effects of caregiving on top of living with an individual with dementia symptoms.; Methods: Census records, providing information on household structure, intensity of caregiving, presence of dementia symptoms and self-reported mental health were linked to mortality records over the following 33 months. Multi-level regression models were constructed to determine the risk of poor mental health and death in co-resident caregivers of individuals with dementia symptoms compared with co-resident non-caregivers, adjusting for the clustering of individuals within households.; Results: The cohort consisted of 10 982 co-residents (55.1% caregivers), with 12.1% of non-caregivers reporting poor mental health compared with 8.4% of intense caregivers (>20 h of care per week). During follow-up, the cohort experienced 560 deaths (245 to caregivers). Overall, caregiving co-residents were at no greater risk of poor mental health but had lower mortality risk than non-caregiving co-residents (adjusted odds ratio (ORadj) = 0.93, 95% confidence interval (CI) 0.79, 1.10 and ORadj = 0.67, 95% CI 0.56, 0.81, respectively); this lower mortality risk was also seen amongst the most intensive caregivers (ORadj = 0.65, 95% CI 0.53, 0.79).; Conclusion: Caregiving poses no additional risk to mental health over and above the risk associated with merely living with someone with dementia and is associated with a lower mortality risk compared with non-caregiving co-residents.