ObjectiveThis study aims to identify whether pain and dementia-related behavior are associated with different types of activities in nursing home residents, controlled for dementia severity. DesignCross-sectional baseline data from the multicomponent cluster randomized controlled COSMOS trial (acronym for Communication, Systematic pain treatment, Medication review, Organization of activities, and Safety). Setting and ParticipantsA total of 723 patients from 33 Norwegian nursing homes with 67 units (clusters). Participants aged ≥65 years, with a life expectancy of >6 months, and with valid data on activity were eligible for inclusion. MethodsActivity was operationalized in time (hours per week) and type (cognitive, social, physical, and no activity). Cognitive function was assessed using the Mini-Mental State Examination (MMSE), pain with the Mobilization-Observation-Behavior-Intensity-Dementia-2 Pain Scale (MOBID-2), and behavior with the Neuropsychiatric Inventory Nursing Home version (NPI-NH). Analyses were performed using linear and logistic regression. Sensitivity analyses for dementia severity were performed to account for effect modification. ResultsA total of 289 participants were included (mean age 86.2 [SD 7.6]; 74% female). A higher pain score was associated with less time spent on activity in participants with severe dementia (estimate 0.897, P = .043). A higher score for the NPI-NH mood cluster (depression and anxiety) was associated with a higher likelihood of participation in cognitive activities (odds ratio [OR], 1.073; P = .039). Apathy (OR, 0.884; P = .041) and lack of inhibition (OR, 0.904; P = .042) were associated with a lower likelihood of participation in social activities as well as no engagement in activities (apathy OR, 0.880; P = .042; lack of inhibition OR, 0.894; P = .034). Conclusion and ImplicationsPain and dementia-related behavior may influence the participation in activities in the nursing home. There is an urgent need to investigate what type of activity stimulates people in different stages of dementia.