Background & aims This study determined the association between phase angle (PhA), by bioelectrical impedance analysis (BIA) and nutritional risk by Nutritional Risk Screening (NRS-2002), Subjective Global Assessment (SGA), hospital length of stay (LOS) and 30 day non-survival in patients at hospital admission compared to healthy controls. Methods PhA was determined by BIA in patients (n = 983, 52.7 ± 21.5 yrs, M 520) and compared to healthy age-, sex- and height-matched controls. Low PhA was set at <5.0° (men) and <4.6° (women) as previously determined (Kyle, in press). Results PhA was lower in patients (men 6.0 ± 1.4°, women 5.0 ± 1.3°) than controls (men 7.1 ± 1.2°, women 6.0 ± 1.2°, un-paired t-test p < 0.001). Patients were more likely to have low PhA than controls: NRS-2002: no risk (relative risk (RR) 1.7, 95th confidence interval (CI) 1.2–2.3), moderate risk (RR 4.5, CI 3.4–5.8) and severe risk (RR 7.5, CI 5.9–9.4); similar results were obtained by SGA; LOS ≥21 days (RR 6.9, CI 5.1–9.1) and LOS 5–20 days (RR 5.2, CI 3.9–6.9) and non-survivors (RR 3.1, CI 2.1–3.4) compared to survivors. Conclusions There is a significant association between low PhA and nutritional risk, LOS and non-survival. PhA is helpful to identify patients who are at nutritional risk at hospital admission in order to limit the number of in-depth nutritional assessments.