Background <p>Isolated iliac artery aneurysms (IIAAs) are exceedingly rare in neonates and infants. Iliac artery aneurysms can be classified into true aneurysms, pseudoaneurysms and entrapment aneurysms. We present a case of an isolated pseudoaneurysm occurring during the perinatal period. The pregnant woman had no family history of genetic disorders or pregnancy-related conditions, and no connective tissue disorders were detected.</p> Case presentation <p>This case illustrates a perinatal diagnosis of an isolated pseudoaneurysm in the iliac artery. Given concerns regarding the potential for aneurysmal rupture, a caesarean section was performed at 37 weeks of gestation. Postpartum contrast-enhanced computed tomography (CT) revealed a mass in the left external iliac artery that significantly compressed the external iliac vein. Computed tomography angiography (CTA) identified an aneurysm adjacent to the iliac artery. The infant remains asymptomatic and is currently undergoing clinical follow-up. clinical observation.</p> Conclusions <p>Prenatal ultrasound can accurately identify isolated iliac aneurysms in the fetus and is thus a highly valuable tool for clinical intervention and treatment.</p>