This study investigated the factors contributing to psychological distress and positive affect over time in female working carers of older people. Questionnaires (including measures of work-related, care-related, interpersonal and psychological aspects of working and caring) were distributed to 275 female working carers in the UK, the majority of whom were working as nurses in the National Health Service. In cross-sectional analyses, higher work stress and work demands predicted higher psychological distress among respondents. Better carer health, lower external pressures to care and higher work satisfaction predicted greater positive affect. The combined effects of greater work stress and work demands also predicted higher levels of psychological distress at follow-up (after one year), whereas younger age and lower work stress predicted greater positive affect over time. We conclude that more stressful and demanding work roles appear detrimental to carers’ mental health, while lower stress occupational roles may be beneficial, providing satisfaction and fulfilment outside of the caring role. Older female carers may be especially at risk of psychological distress, possibly due in part to increasing health problems of their own.