Introduction: Accessory spleen is a congenital defect characterised by a separated ectopic splenic parenchyma usually located in the splenic hilum and the tail of the pancreas. It is present in about 10%–30% of the population and, generally, does not cause any symptoms. Case report: We report an interesting case of a woman with symptomatic intramesenteric accessory spleen detected and characterised by contrast-enhanced ultrasound. The patient experienced a long history of intermittent pain in the left upper abdomen. The diagnosis was confirmed by post-operative pathology examination. Discussion: Accessory spleen usually appears as a well-circumscribed ovoid mass, 1–3 cm in diameter, infrequently located in the mesentery. It may rarely become symptomatic because of complications. Diagnosis of this condition as a cause of abdominal is difficult and rarely has been made pre-operatively. Computed tomography and magnetic resonance imaging might help, but they should be performed with intravenous contrast injection, and they cannot provide direct evidence between the pain of the patient and the lesion. Conversely, real-time ultrasound can assess and diagnose the lesion showing the exact correspondence with abdominal pain of the patient. Furthermore, ultrasound and contrast-enhanced ultrasound are widely available, safe and relatively inexpensive. Conclusion: Apart from the rarity of this condition, this case report demonstrates the ability of ultrasound to localise the intramesenteric accessory spleen, assess the relationship between the lesion and the symptoms of the patient, and characterise the lesion.