ABSTRACT: Acute primary peritonitis in the absence of other comorbid conditions such as liver cirrhosis, immunosuppression, or nephrotic syndrome is a rare disorder in young adults. In women, ascending genital infections are thought to be a major pathogenic cause of this type of peritonitis. Pus was detected in the peritoneal cavity by abdominal paracentesis in a 27-year-old woman who had no predisposing features for severe peritonitis. Abdominal computed tomography showed perirectal edema. Laparotomy was performed, but no intra-abdominal focus of infection could be detected. The abdomen was irrigated via a subhepatic and retroperitoneal presacral approach, and broad-spectrum antibiotic therapy was started. Blood cultures revealed group A streptococci, usually a common cause of upper respiratory tract infections or erysipelas. Within a few days, the patient recovered completely and returned to normal life. (American Journal of Critical Care. 2010;19:454–458) : Cases of Note features peer-reviewed case reports and case series that document clinically relevant findings from critical and high acuity care environments. Cases that illuminate a clinical diagnosis or a management issue in the treatment of critically and acutely ill patients and include discussion of the patientʼs experience with the illness or intervention are encouraged. Proposals for future Cases of Note articles may be e-mailedtoajcc@aacn.org.