Purpose: To examine the impact of changes in an older person's frailty on the care-related quality of life of their informal caregiver.; Methods: Five research projects in the TOPICS-MDS database with data of both older person and informal caregiver at baseline and after 12 months follow-up were selected. Frailty was measured in five health domains (functional limitations, psychological well-being, social functioning, health-related quality of life, self-rated health). Care-related quality of life was measured with the Care-Related Quality of Life instrument (CarerQoL-7D), containing two positive (fulfilment, perceived support) and five negative dimensions (relational problems, mental health problems, physical health problems, financial problems, problems combining informal care with daily activities).; Results: 660 older person/caregiver couples were included. Older persons were on average 79 (SD 6.9) years of age, and 61% was female. Caregivers were on average 65 (SD 12.6) years of age, and 68% was female. Results of the multivariable linear and logistic regression analyses showed that an increase in older person's frailty over time was related to a lower total care-related quality of life of the caregiver, and to more mental and physical health problems, and problems with combining informal care with daily activities at follow-up. A change in the older person's psychological well-being was most important for the caregiver's care-related quality of life, compared to the other health domains.; Conclusions: Health professionals observing decreasing psychological well-being of an older person and increasing hours of informal care provision should be aware of the considerable problems this may bring to their informal caregiver, and should tailor interventions to support informal caregivers according to their specific needs and problems.