BACKGROUND Existing literature has detailed occurrences of retroperitoneal yolk sac tumors (YSTs) as the result of metastasis from a primary gonadal site. However, primary retroperitoneal YSTs are extremely rare, thus remaining a challenge to diagnose and treat. We present a complex case of a large primary retroperitoneal YST in a man treated with neoadjuvant chemotherapy followed by surgical resection. CASE REPORT A 31-year-old man presented with a chief symptom of severe lower abdominal pain. Diagnostic imaging revealed a large, rapidly progressing neoplasm in the retroperitoneal region, initially thought to be a sarcoma. However, the pathological results from further biopsies found the mass to be a retroperitoneal YST, which was tethered to a large portion of the small bowel. A testicular ultrasound was used to confirm that the mass was a primary tumor with no origins in the gonads. The tumor progressed to involve several fistulas connected to the small intestine and anterior abdominal wall. The patient was treated with 3 cycles of bleomycin, etoposide, and cisplatin, followed by surgical excision of the residual mass. The patient retained normal gastrointestinal functions, and subsequent imaging revealed no evidence of recurrence 2.5 years following resection. CONCLUSIONS Owing to the rarity of extragonadal primary YSTs, diagnostic and treatment standards have not yet been sufficiently explored. Our case demonstrates that a combination of chemotherapy and surgical resection should be considered for select patients with primary YST in the retroperitoneal region.