We report the case of a 68-year-old woman with a cellular schwannoma in the retroperitoneum, which recurred 16 months after resection. This rare tumor is generally considered as benign in spite of its pseudosarcomatous histologic appearance. Immunohistochemical positivity for S-100 protein is very useful for the diagnosis. Recommended treatment is surgical excision but incomplete resections can be followed by recurrences.