Background In the UK, it is recommended that hospital patients have their nutritional status assessed within 24 h of admission using the Malnutrition Universal Screening Tool (MUST). The present study aimed to examine the association between nurse staffing levels and missed nutritional status assessments. Methods A single‐centre, retrospective, observational study was employed using routinely collected MUST assessments from 32 general adult hospital wards over 2 years, matched to ward nurse staffing levels. We used mixed‐effects logistic regression to control for ward characteristics and patient factors. Results Of 43 451 instances where staffing levels could be linked to a patient for whom an assessment was due, 21.4% had no MUST score recorded within 24 h of admission. Missed assessments varied between wards (8–100%). There was no overall association between registered nurse staffing levels and missed assessments; although higher admissions per registered nurse were associated with more missed assessments odds ratio (OR) = 1.09, P = 0.005. Higher healthcare assistant staffing was associated with lower rates of missed assessments (OR = 0.80, P < 0.001). There was a significant interaction between registered nurses and healthcare assistants staffing levels (OR = 0.97, P = 0.011). Conclusions Despite a written hospital policy requiring a nutritional assessment within 24 h of admission, missed assessments were common. The observed results show that compliance with the policy for routine MUST assessments within 24 h of hospital admission is sensitive to staffing levels and workload. This has implications for planning nurse staffing. Negative patient outcomes associated with malnutrition in hospital patients can be avoided by ensuring that every patient has a nutritional assessment completed and recorded, leading to appropriate interventions aimed at avoiding preventable deterioration. However, research shows missed nutritional assessments with lower levels of nurses in hospital wards. The findings from an observational study using administrative routinely collected data on the prevalence of missed nutritional assessments in a hospital in England show that compliance with the policy for routine Malnutrition Universal Screening Tool (MUST) assessment within 24 h of hospital admission is sensitive to staffing levels and workload. This has implications for planning nurse staffing.