Informal care is a central pillar of English social care policy. Cross-sectional research has found significant associations between caregiving and poor sleep. Insufficient and disturbed sleep is increasingly associated with negative health outcomes among older adults. Among caregivers it has been associated with reduced quality of life, and cited as a significant reason for cessation of caregiving. Yet there has been limited longitudinal research to date. This study investigates longitudinal associations between co-resident caregiving and problematic sleep. A sample of 2,494 co-resident caregivers and non-caregivers aged 65 years and older was drawn from the UK Household Longitudinal Study. Problematic sleep was defined as two or more problems in going to sleep, staying asleep or sleep quality. Logistic regression was used to investigate patterns in co-resident caregiving and problematic sleep, in the context of a modified Caregiver Stress Framework. Caregiving intensity and transitions were also examined, adjusting for potential confounding and mediating factors. Co-resident caregivers were 1.47 (CI 0.95: 1.06-2.03) times more likely to report problematic sleep than those providing no care, adjusted for baseline sleep, gender and subjectively perceived health. Continuous caregiving over a one- and three-year period also showed significantly increased odds of problematic sleep, adjusted for baseline sleep and gender. Entry into and exit from caregiving were not significantly associated with sleep. Older co-resident caregivers are at greater risk of incurring sleep problems than non-caregivers. Further longitudinal studies are needed to explore a wider range of possible factors leading to problematic sleep, and investigate its caregiver-specific consequences.