Disseminated actinomycosis is uncommon in the pediatric population and rarely presents as a renal mass mimicking a renal tumor with metastases. Diagnosis may be difficult. In this case, percutaneous biopsy results only showed necrosis and fibrosis and, hence, were not helpful in diagnosis. Exploratory laparotomy and open biopsy results showed that this renal tumor was an actinomycotic abscess with similar abscesses in the liver and lung masquerading as metastases. The treatment for disseminated actinomycosis is with parenteral and oral penicillin. Copyright (C) 2001 by W.B. Saunders Company.