Background: Depression in informal caregivers of persons with dementia is a major, costly and growing problem. However, it is not yet clear which caregivers are at increased risk of developing depression. With this knowledge preventive strategies could focus on these groups to maximize health gain and minimize effort. Methods: The onset of clinically relevant depression was measured with the Center for Epidemiologic Studies-Depression Scale in 725 caregivers who were not depressed at baseline and who were providing care for a relative with dementia. Caregivers were followed over 18 months. The indices calculated to identify the most important risk indicators were: odds ratio, attributable fraction, exposure rate and number needing to be treated. Results: The following significant indicators of depression onset were identified: increased initial depressive symptoms, poor self-rated health status and white or Hispanic race/ethnicity. The incidence of depression would decrease by 72.3% (attributive fraction) if these risk indicators together are targeted by a completely effective intervention. Race/ethnicity was not a significant predictor if caregivers of patients who died or were institutionalized were left out of the analyses. Conclusion: Detection of only a few characteristics makes it possible to identify high-risk groups in an efficient way. Focusing on these easy-to-assess characteristics might contribute to a cost-effective prevention of depression in caregivers. © 2011 International Psychogeriatric Association.