Objectives: To characterize dietary habits and eating patterns in patients with a urea cycle disorder (UCD), and to identify dietary habits that may serve as clues to lead to earlier diagnosis of these disorders. Study design: This was a retrospective study of clinical and dietary data from hospital records of all patients with UCD (n = 90) attending the Royal Children's Hospital in Melbourne between 1972 and 2010. Results: Protein aversion, food refusal, frequent vomiting, poor appetite, and adverse reaction to high-protein-containing foods were documented in the majority of patients with available detailed dietary protein intake data. Fourteen of the 90 admissions for metabolic deterioration in which information regarding the precipitating factor(s) were available were directly related to protein intake (5 higher and 9 lower than prescribed). Conclusion: Protein aversion is a common feature of UCD and may serve as a diagnostic clue in patients presenting with food refusal, recurrent vomiting, behavioral problems, mental retardation, and "unexplained" episodes of altered consciousness. Dietary history should be included in the investigation of these symptoms, which might lead to earlier diagnosis. Metabolic decompensation is more frequently related to low energy/protein intake than to high protein intake in these patients. Special attention should be given to protein aversion, which often leads to eating patterns that make it difficult for a patient to achieve the prescribed daily protein requirement.