Introduction: Little is known about the raising number of specialized units for patients with dementia and very severe challenging behavior in the Netherlands. This study describes organizational and treatment characteristics of a sample of these units. Methods: The organizational and treatment characteristics were studied with digital questionnaires completed by the unit managers, interviews with the main physician(s) and observation of the physical environment. The questionnaire consisted of questions about general patient characteristics, unit characteristics and staff characteristics. Furthermore, an interview was held with the main/treating physician often together with another physician or psychologist. The interview guide consisted of questions about admission criteria, the role of staff involved and the treatment process. Results: Thirteen units participated. Five units were part of a mental health (MH) institution, seven units were part of a nursing home (NH) organization and one unit was a cooperation of MH and NH. Unit sizes ranged from 10 to 28 places. Ten of thirteen units started in 2010 or later. The age of patients admitted was estimated at 75 years. The percentage of involuntary admitted patients was 53% at MH-units and 18% at NH-units. Unit managers mentioned that due to a difference in reimbursement between MH and NH units had difficulty providing the specialized care. Another problem managers faced was recruiting nursing staff. Units strived for expertise in general staffing from both MH and NH. The education level of the nursing staff was comparable between MH and NH. At every unit a physician with background in elderly care medicine or geriatrics and a psychiatrist was involved. Interviewees stressed the role of the nursing staff in the treatment. They were key in providing the care and treatment that, since the main goal of interventions is treatment of and coping with challenging behavior. Conclusion: The main finding of this study is that units caring for patients with dementia and ...