Any medical treatment that interferes with physical integrity requires the informed consent of a patient capable of such consent. For people with dementia, the capacity to consent is questioned even in the early course of the disease. Particularly diagnostic instruments like the MacArthur Competence Assessment Tool for Treatment (MacCAT-T) often deny people with dementia the capacity to consent because of high confounding of the results with patients’ verbal abilities. To date, it remains unclear whether not only verbal but also nonverbal communication is associated with assessments of capacity to consent. The current study investigates associations between patients’ verbal and nonverbal communication behaviors as assessed by the measure for Communication Behavior in People with Dementia in Ambulant Settings (CODEMamb) and capacity to consent as assessed by the MacCAT-T. We expected the strongest positive associations for verbal communication behaviors compared to nonverbal communication behaviors. Data of N = 43 patients with dementia ( n = 8 capable of consent) were collected at two different German psychiatric clinics. The results show small to moderate correlations between the overall scores of CODEMamb and MacCAT-T. As expected, correlations were strongest for the verbal CODEMamb subscale. The results support current findings on the dependency of the MacCAT-T on verbal communication. Based on the findings, the discussion addresses how people with dementia can be enabled to make self-determined medical treatment decisions.