Background: Caring for a person with Alzheimer's disease (AD) is associated with significant mental burden e.g., depression and anxiety, and difficulties with social, familial, and professional functioning. To date, few studies have examined variables which would allow for a comprehensive and detailed study of the relationship between personal resources and caregiver health status, with a majority of studies focusing on factors that contribute to increased caregiver's burden. Moreover, the available evidence fails to address differences in the functioning of formal and informal carers. Paying proper attention to the problems of nursing home staff can help identify important risk factors. Therefore, this study compared mental health problems in informal and formal caregivers and examined the relationship between mental resources and mental health problems in both groups of caregivers. Methods: This cross-sectional study examined 100 formal (n = 50) and informal (n = 50) caregivers of AD patients. Personal resources were measured with the Social Support Questionnaire (SSQ), the Generalized Self-Efficacy Scale (GSES), and the Sense of Coherence Questionnaire (SCQ), while mental health was assessed with the Depression Assessment Questionnaire (DAQ) and the General Health Questionnaire (GHQ). Multivariate stepwise regression was performed separately for both investigated groups. Results: There were no significant differences between informal and formal caregivers in terms of psychological variables, i.e., sense of coherence, social support, self-efficacy, or mental health problems. In contrast, there were different significant predictors of mental health problems in both groups. Comprehensibility (SCQ) was a significant predictor of mental health problems measured by DAQ and self-efficacy (GSES) was a significant predictor of mental health problems measured by GHQ in informal caregivers. For formal caregivers, emotional support (SSQ) and comprehensibility (SCQ) were significant predictors of mental health problems measured by DAQ, while tangible support (SSQ) and meaningfulness (SCQ) were significant predictors of mental health problems measured by GHQ. Conclusions: Personal resources are significant predictors of mental health outcomes in caregivers of AD patients. Preventive actions should therefore include assessment of factors affecting caregivers' mental health in order to provide them with necessary care and create appropriate support groups.