Background Frailty is a state of vulnerability to poor resolution of homeostasis after a stressor event and is strongly associated with adverse outcomes. Therefore, the assessment of frailty may be an essential part of evaluation in any healthcare encounter that might result in an escalation of care. The purpose of the study was to assess the frequency and association of frailty with clinical outcomes in patients subject to rapid response team (RRT) review. Methods In this multi-national prospective observational cohort study, centres with existing RRTs collected data over a 7-day period, with follow up of all patients at 24 h following their RRT call and at hospital discharge or 30 days following the event trigger (whichever came sooner). Investigators also collected data on the triggers and interventions provided and a bedside assessment on the level of patients’ frailty using a clinical frailty scale. Results Amongst 1133 patients, 40% were screened as frail, which was associated with older age (p < 0.001), admission under a medical speciality (p < 0.001), increased severity of illness at the time of the RRT review (p = 0.0047), and substantially higher frequency of limitations of care (p < 0.001). Importantly, 72% of patients screened as frail were either dead or dependent on hospital care by 30 days (p < 0.001). In the multivariable analysis, the significant risk factors for the composite endpoint “poor recovery” (died or were hospital-dependent by 30 days) were age (odds ratio (OR), 1.04; 95% confidence interval (CI), 1.03–1.05; p < 0.001), frailty level (p < 0.001), existing limitation of care (OR, 2.0; 95% CI, 1.3–3.0; p < 0.001), and the quick sequential organ failure assessment (qSOFA) score (p < 0.001). Conclusions Higher frailty scores were associated with increased mortality and dependence on health care at 30 days. Our results indicate that frailty has an influence on the clinical trajectory of deteriorating patients and that such assessment should be included in discussion of goals and expectations of care.