Abstract Background Older adults are too often hospitalized from the emergency department (ED) without needing hospital care. Knowledge about rates and causes of these preventable emergency admissions (PEAs) is limited. This study aimed to assess the proportion of PEAs, the level of agreement on perceived preventability between physicians and patients, and to explore their underlying causes as perceived by patients, their relatives, and the admitting physician. Methods A multi-center multi-method study at the ED of one academic and two regional hospitals in the Netherlands was performed. All patients aged > 70 years and hospitalized from the ED were consecutively sampled during a six-week period. Quantitative data regarding patient and clinical characteristics and perceived preventability of the admission were prospectively collected from the electronical medical record and analyzed using descriptive statistics. Agreement on preventability between patient, caregivers and physicians was assessed by using the Cohen’s kappa. Underlying causes of a PEA were subsequently collected by semi-structured interviews with patients and caregivers. Physician’s perceived causes of a PEA were collected by telephone interviews and by open-ended questions sent by email. Thematic content analysis was used to analyze the interview transcripts and email narratives. Results Out of 773 admissions, 56 (7.2%) were deemed preventable by patients or their caregivers. Admitting physicians regarded 75 (9.7%) admissions as preventable. The level of agreement between these two groups was low with a Cohen’s kappa score of 0.10 (p = 0.003). Perceived causes for PEAs related to six themes: (1) insufficient support at home, (2) suboptimal care in the community setting, (3) errors in hospital care, (4) time of presentation to ED and availability of resources, (5) delayed help seeking behavior, and (6) errors made by patients. Conclusions Our findings contribute to the existing evidence that a substantial part (almost one out of ten) of the ...