A 39‐year‐old woman underwent emergency cesarean section (CS) due to placenta previa totalis with massive bleeding. Two major problems emerged in this patient after CS was carried out. One was partial retention of the placenta due to placenta accreta. Another major and more serious problem was pyoderma gangrenosum (PG) widely appearing at the skin of the abdomen around the CS wound. Conservative treatment was performed for the retained placenta, and it had completely disappeared by 76 days after the CS. The diagnosis of PG was promptly made in consultation with a plastic surgeon and a dermatologist when a wide ulcer emerged around the CS wound, and high‐dose prednisolone was administered as treatment. At 90 days following the CS, near‐complete epithelialization was achieved. This extremely rare case reflects the importance of rapid diagnosis and treatment of PG.