The purpose of this paper is to describe the development and initial piloting of a Functional Status Assessment of Seniors in Emergency Department (FSAS-ED). The methodology of development of the tool included (1) specifying the underlying construct based on the conceptual framework of the International Classification of Functioning, Disability and Health (ICF), (2) deciding on an interview-based format appropriate for addressing functioning pre- and post-ED, (3) developing an initial 63-item pool and reviewing it through a consensus group with seven experts, (4) piloting the prototype with 23 subjects (mean age=76 years) and (5) subsequently revising its rating scales. The final 40 items tool consists of three theoretically derived components. First, activity and participation (n=23 items) address nine ICF domains using a 4-level scale combining levels of difficulty and help required. Second, body functions (n=10 items) cover eight ICF domains with a 3-level scale of impairment. And third, environmental factors (n=7 items) address four ICF domains assessed as facilitators or barriers. In conclusion, the FSAS-ED provides a clinical assessment of senior's functional status that is feasible to use in ED. It has potential utility for identifying unmet needs and obstacles for a safe return to the community.