Abstract Purpose We evaluated the level of oral hygiene and its association with oral health status and need for oral treatment among older residents in long-term care facilities. In addition, the association between oral hygiene level and health-related quality of life (HRQoL) was explored. Methods This cross-sectional study assessed 231 dentate residents in long-term care facilities (71% female, mean age 81 years, 70% had dementia). Nurses assessed residents and completed questionnaires on participants’ background information, diagnoses, oral healthcare habits, and HRQoL with the 15D instrument. Two qualified dentists performed clinical oral examinations (number of teeth, plaque index, periodontal condition, open caries lesions, and dry mouth). We used a modified plaque index (PI) to measure the level of oral hygiene (good, moderate, and poor) and calculated the clinical Asymptotic Dental Score (ADS) to determine the oral inflammation burden. Results Of the residents, 21% had good, 35% moderate, and 44% poor oral hygiene according to PI. Poor oral hygiene was associated with poorer cognitive status (P = 0.010) and higher oral inflammation burden (P < 0.001). Moreover, poor oral hygiene was associated with poorer HRQoL in a correlation analysis adjusted for age and gender. Conclusions Oral hygiene of older individuals in long-term care is insufficient. Poor oral hygiene is a marker for poor HRQoL. Residents also have a high burden of oral inflammatory diseases and a need for dental care. Older residents’ oral hygiene and HRQoL may be improved with oral care education of caregivers and regular dental check-ups.