Objectives: To explore and compare levels of mental health, care burden, and relationship satisfaction among caregiving spouses of people with mild cognitive impairment or dementia in Parkinson disease (PD-MCI or PDD) or dementia with Lewy bodies (DLB). Methods: Spouses (n = 136) completed measures of mood, stress, resilience, general health, quality of life, care burden, and relationship satisfaction, as well as sociodemographic factors. Additionally, data on motor and neuropsychiatric symptom severity of people with PD-MCI, PDD, or DLB were obtained in a subsample. Results: Most spouses were married women (>85%) who provided a median of 4 years of care and 84 hours of weekly care. Among these, relationship dissatisfaction, stress, anxiety, care burden, and feelings of resentment were common. Spouses of people with PDD and DLB had significantly higher rates of burden, resentment, and depression compared to spouses of people with PD-MCI. Furthermore, unique group differences emerged whereby spouses of people with PDD had significantly longer duration of care provision, higher stress, more relationship dissatisfaction, and fewer positive interactions, compared to PD-MCI group, whereas anxiety and lower levels of mental health were prominent in spouses of people with DLB, compared to PD-MCI group. Despite this, the majority of spouses reported good quality of life, resilience, and satisfaction with the caring role. Conclusion: Both PDD and DLB significantly contribute to poorer mental health and higher levels of care burden in spouses. Clinicians should actively screen the risk of burden, stress, depression, and anxiety among caregiving spouses of people with these conditions.