Abnormal eating behaviour among psychiatric patients is associated with several psychiatric conditions, but may also be caused by a comorbid physical condition. Clinical assessment of a psychiatric patient is often challenging, which contributes to an increased rate of undiagnosed medical conditions and an increased mortality rate. We present the clinical case of a 46-year-old woman with a long-term delusion of triplet pregnancy, and recurrent vomiting. She experienced intense weight loss and eventually faced a life-threatening situation due to achalasia, which was incidentally discovered on a chest X-ray during her second psychiatric hospitalization, after several other tests, including upper digestive endoscopy, returned normal results. After a successful laparoscopic Heller's myotomy, her digestive symptoms greatly improved. This report illustrates the difficulty of establishing clinical-surgical diagnoses in psychotic patients, as some delusions seem to explain clinical complaints, masking and delaying the diagnosis of comorbid conditions.