Screening patients' nutritional status on admission to hospital is recommended by evidence-based guidelines on malnutrition. In practice, self-reported values for body weight and height are often used by nurses and dieticians. This study assessed the accuracy of self-reported body weight and height and whether these self-reported values might be influenced by the nature of the health-care worker involved. Patients (n = 611) on admission reported their body weight and height to a nurse and a dietician. Reported values were analysed and compared with the measured values. Self-reported values for body weight and height on admission are not always accurate. Patients do report different values to different health-care workers. Self-reported values for body weight to nurses were more accurate as compared with dieticians. Self-reported values for body weight and height are subject to observer bias and should be used with caution in nutritional screening and multi-professional nutritional care.