A 12-year-old girl presented with significant vomiting, and generalised muscular weakness. She had normal anion gap metabolic acidosis, hypokalemia and alkaline urine. Vomiting generally leads to metabolic alkalosis but this patient had acidosis which suggested either renal tubular acidosis (RTA) or diarrhoea. Investigations showed distal RTA. There was no family history of similar illness. Abdominal ultrasound showed features of the superior mesenteric artery syndrome, but a barium study showed no duodenal obstruction, making this an unlikely cause of symptoms. Weight loss as a result of the renal condition may have caused loss of mesenteric or retro-duodenal fat and explain the ultrasound appearance.