Background. Although religious delusions (RDs) are common in geriatric psychiatry, we know little about their frequency and content. Our study examines the prevalence and content of religious hallucinations (RHs) and RDs and how they relate to the diagnosis and the patients’ denominational background and other aspects of religiousness. Methods. Semi-structured diagnostic interviews were conducted with inpatients and outpatients (N = 155, mean age 76.5) at a geriatric psychiatry department in the Netherlands. We used the Schedules for Clinical Assessment in Neuropsychiatry 2.1. Results. The prevalences of RHs and RDs were 19% and 32%, respectively. RHs were mostly auditory. There was no statistically significant difference between the prevalence of RHs in schizophrenia (17.5%) and in psychotic depression (9.4%). Compared to non-affiliated patients and mainline Protestants, RDs were significantly more prevalent in raised and current strict Protestants, especially in those with psychotic depression. RHs were more prevalent in Evangelical (e.g., Pentecostal) and strict Protestant patients. The presence of RDs was associated with several measures of religiousness (e.g., dogmatism, religious coping). Conclusions. Religion is likely to act as a symptom-formation factor for psychotic symptoms in strict Protestant older adults. More detailed research might lead to a fuller understanding of how strict religious beliefs may affect the content of psychotic symptoms and unintentionally add a component of existential suffering. It is important for mental health professionals, especially the predominantly secular professionals in the Netherlands, to recognize and address religious themes.