This paper reports on the concurrent validity of the Balance Outcome Measure for Elder Rehabilitation (BOOMER) while investigating balance, mobility, and perceived confidence to undertake daily activities experienced by patients at discharge from an Internal Medicine Unit; and seeks to determine if there are differences between patients discharged to rehabilitation to those discharged to their usual residence. Forty-four adults (30 female) average age 77 (SD 7) years, admitted with an acute illness to hospital consented to participate in this study. Balance was measured using the BOOMER and the Berg Balance Scale (BBS). Mobility was measured using the de Morton Mobility Index (DEMMI) and participants' perceived confidence in balance to undertake daily activities determined using the Activities-specific Balance Confidence (ABC) scale. BOOMER scores were highly associated with BBS scores (r = .93, p < 0.001) and raw DEMMI scores (r = .89, p < 0.001) while moderate associations with perceived confidence (r > .52, p < 0.001) were determined. Participants discharged to their usual residence had significantly higher balance and mobility scores compared to those requiring further rehabilitation; no difference was found for ABC scores. Concurrent validity of the BOOMER, BBS and DEMMI was established, supporting use of these tools to measure balance and mobility of patients at discharge from acute care.