Retroperitoneal fasciitis is a progressive infection involving the retroperitoneal fascial planes and deeper soft tissues, requiring prompt diagnosis. A 20-year-old man in India with a history of perianal abscess presented with fever, swelling, and severe pain in the abdomen and inguinoscrotal region. Local examination revealed extensive necrotic skin changes involving the perineum and right lumbar region, extending to the scrotum. Contrast-enhanced computed tomography demonstrated a large myocutaneous defect with extensive air foci, fat stranding, and fluid collections in the abdominal wall extending into both retroperitoneal spaces. The patient underwent emergency surgery with debridement of the perineum and right lumbar region. Vacuum-assisted closure therapy and local sump application facilitated rapid and effective wound healing, eliminating the need for reconstruction. This case illustrates successful management of a rare but severe condition.