Castleman's disease is presented in the following article in more detail using the case report of a 55-year-old patient with abdominal pain without any significant pre-existing medical conditions. A computer tomography of the abdomen demonstrated a retroperitoneal tumor in the lower abdomen below the aortic bifurcation. Because malignancy of the tumor could not be excluded, surgical extirpation was performed without complications. Histopathological examination revealed the diagnosis of a localized castleman's tumor. Castleman's disease is a rare disease of the lymph nodes of unknown etiology. In the prognosis, benign forms can be distinguished from malignant forms.