A1-year-old infant presented to our hospital with a pelvic mass. There was no history of surgery, and the clinical examination revealed a pelvic palpable lesion. Magnetic resonance imaging showed a pelvic mass that was heterogeneous on T1-weighted and T2-weighted images, and it was heterogeneously enhanced after contrast administration (Fig. 1). Magnetic resonance images showed the involvement of the sacral vertebrae, and the mass compressed the bladder and extended into the lumbar medullary canal (Fig. 2). The mass was surgically removed, and it was identified as a yolk sac tumor via pathologic examination.