Background The majority of residents in care homes in the United Kingdom are living with dementia or significant memory problems. Caring in this setting can be difficult and stressful for care staff who work long hours, have little opportunity for training, are poorly paid and yet subject to high expectation. This may affect their mental and physical wellbeing, cause high rates of staff turnover and absenteeism, and affect the quality of care they provide. The main objective of this survey was to explore the nature, characteristics and associations of stress in care home staff. Methods Staff working in a stratified random sample of care homes within Wales completed measures covering: general health and wellbeing (SF-12); stress (Work Stress Inventory); job content (Karasek Job Content); approach to, and experience of, working with people living with dementia (Approaches to Dementia Questionnaire; and Experience of Working with Dementia Patients); and Productivity and Health Status (SPS-6). Multiple linear regressions explored the effects of home and staff characteristics on carers. Results 212 staff from 72 care homes completed questionnaires. Staff from nursing homes experienced more work stress than those from residential homes (difference 0.30; 95% confidence interval (CI) from 0.10 to 0.51; P < 0.01), and were more likely to report that their health reduced their ability to work (difference -4.77; CI -7.80 to -1.73; P < 0.01). Psychological demands on nurses were higher than on other staff (difference = 1.57; CI 0.03 to 3.10; P < 0.05). A positive approach to dementia was more evident in those trained in dementia care (difference 8.54; CI 2.31 to 14.76; P < 0.01), and in staff working in local authority homes than in the private sector (difference 7.75; CI 2.56 to 12.94; P < 0.01). Conclusions Our study highlights the importance of dementia training in care homes, with a particular need in the private sector. An effective intervention to reduce stress in health and social care staff is required, especially in nursing and larger care homes, and for nursing staff.