Persistent descending mesocolon is an uncommon developmental anomaly which results from failure of fusion of the descending mesocolon with the posterior parietal peritoneum. It is asymptomatic in most cases and rarely causes intestinal obstruction. We report here a case of primary intestinal obstruction complicated by a persistent descending mesocolon. A 66-year-old man without prior laparotomy was admitted with a diagnosis of small bowel obstruction. Pre-operative investigation demonstrated a segmental jejunal stenosis and a persistent descending mesocolon as possible causes of the obstruction. Laparotomy showed that the cause of the obstruction was the jejunal stenosis, not the persistent descending mesocolon. The stenosis was resected, but correction of the anomaly was not performed. The patient made an uneventful recovery after the operation. From our limited experience, persistent descending mesocolon need not be surgically corrected when it is not considered to be the cause of obstruction and another definite cause co-exists.