Actinomycosis is an uncommon disease in children and most cases are cervicofacial infections. To date, there have been only a few reports on children with chest wall involvement due to actinomycosis. Here we report a 9-year-old girl with a mass lesion in the chest wall mimicking Ewing's sarcoma of the rib. Thoracic actinomycosis without typical features of the disease is often evaluated with the suspicion of neoplasia. This rare entity should be considered in the differential diagnosis of mass lesions of the chest wall in children. The disease responds well to penicillin treatment.