Abstract Background: Rhizobium radiobacter rarely causes human infections, most of which develop in immunocompromised patients, and especially those with intravenous catheters. Although R. radiobacter has been reported in association with peritonitis, all such reported cases have been due to intra-peritoneal devices in patients undergoing peritoneal dialysis. Herein we report the first case of a perforated ulcer complicated by peritonitis caused by R. radiobacter in a healthy adult, which was treated successfully with surgery and antibiotics. Methods: Case report and literature review Results: A 33-year-old male presented with epigastric abdominal pain of sudden onset. Physical examination was unremarkable except for the finding of diffuse abdominal tenderness with rebound tenderness. Exploratory laparotomy revealed a perforated duodenal ulcer with secondary peritonitis. The patient underwent pyloroplasty with bilateral truncal vagotomy and peritoneal toilet. Turbid ascites was sent for culture and yielded R. radiobacter and Streptococcus viridans. The patient was treated with a 10-d course of ceftazidime on the basis of drug susceptibility results, and recovered completely without complications. Conclusions: We report a case of secondary peritonitis caused by R. radiobacter , which expands the spectrum of infectious diseases caused by this organism.