Anorectal necrosis is an uncommon lethal disease in children, characterized by necrosis of the mucosa of the anus and rectum. The difference between anorectal necrosis and Fournier’s gangrene is that anorectal necrosis does not affect the genital organs. The treatment for anorectal necrosis includes debridement of the anus, colostomy, and the use of broad-spectrum antibiotics. However, anorectal necrosis may lead to anal stricture, anal malfunction, or even acquired atresia of the anus. There is no consensus on the treatment for acquired imperforate anus. Herein, we report a case of a four-month-old boy with acquired imperforate anus complicated by anorectal necrosis. We describe our experience performing posterior sagittal anorectoplasty to reconstruct a neo-anus in such a rare case.