The objectives of the present cross-sectional study were to assess the screening, prevalence and management of malnutrition and identify any co-existence with obesity in adult hospital in-patients. The Malnutrition Universal Screening Tool (MUST) was applied to all medical, surgical, orthopaedic and critical care in-patients in an acute hospital in North-East England on a single day in 2007. An audit was also performed of malnutrition screening using a locally developed tool. Patients were excluded from study if they had been an in-patient less than 24 h or if discharged on the day of study. Of 328 patients meeting inclusion criteria, 100 % had full data collection (143 males, 185 females, median length of stay 8 d (range 1–90 d), median age 76 years (range 17–101 years)). Only 226 patients (68·9 %) had been screened for malnutrition and thirty-one (13·7 %) were at highest malnutrition risk, of which only 45·2 % were appropriately referred to nutrition and dietetic services. The prevalence of malnutrition (MUST ≥ 1) was 44 %. The prevalence of highest risk (MUST ≥ 2) increased with age (20·6 % < 60 years, 29·7 % 60–79 years and 39·4 % ≥ 80 years). In total 37·8 % (n 70) of female patients had a MUST score of ≥ 2 compared with 24·5 % (n 35) of males. Obesity (BMI >30 kg/m2) was identified in 9·5 % of those with a MUST score ≥ 2. We have shown that malnutrition is a common problem affecting over 40 % of patients in this hospital-wide study. Currently malnutrition is often unrecognised and undertreated in clinical practice. Hospitals must develop comprehensive strategies to both identify and treat in-patients with this common condition.