Objectives To develop a feasible and safe prehospital decision support system (DSS) for the emergency medical services (EMS), facilitating safe steering of geriatric patients to an optimal level of healthcare. Methods The development process involves four consecutive steps. The first step was gathering data from patients transported by EMS, with the electronic patient care record, to retrospectively identify appropriate patient categories for steering. The second step was to allow a group of medical experts to give advice and suggestions for further development of the DSS. The third step was validation of the decision support tool and the fourth step was validation of the entire prehospital DSS in a pilot study. Results The patient categories relevant to steering were those medical conditions that the geriatric clinicians felt confident in receiving from the EMS. A prehospital DSS was then developed for these 11 medical conditions. The evaluation and validation of the DSS showed a high degree of compliance with the patients’ final level of healthcare. The pilot study included 110 randomized patients; 33.9% were triaged to an alternative level of healthcare, that is geriatric care or primary care. No medical inaccuracies or secondary transports from alternative care to the hospital emergency department were identified. Conclusion Using this prehospital DSS – developed for 11 medical conditions – the Swedish prehospital nurse can safely decide on the level of healthcare to which an elderly patient can be steered. Keywords: ambulance, assessment, emergency medical service, geriatrics, prehospital nurse, triage