Soft tissue sarcomas are rare neoplasms, which account for less than 1% of adult malignancies. In addition, they account for only 2% of renal cancers. The main mesenchymal lesions of the kidney are benign and difficult to differentiate with well-differentiated sarcomas. The aim of this report was to present the experience of the Hospital Sao Paulo (HU/UNIFESP) in a case of well-differentiated liposarcoma, which affected the kidney of a young adult who has been treated with radiotherapy in childhood, as well as to raise the relevant literature. A 26-year-old male patient with a history of prostate rhabdomyosarcoma that has been submitted to surgical resection and adjuvant radiotherapy 23 years ago in the childhood was presented. He was asymptomatic during 22 years, then he developed back pain, and underwent investigation and one tumor was detected in the right kidney. Radical nephrectomy was performed with complete resection of the lesion and he is currently without evidence of disease recurrence. Renal liposarcoma usually has good prognosis and the treatment is based almost exclusively on tumor resection. The differentiation between primary renal or retroperitoneal site is important for the prognostic assessment of the disease. There is a relationship between exposure to radiation in childhood and the development of second malignancy in adulthood, especially soft tissue sarcomas. Metastases are rare in well-differentiated forms of the disease. Recurrences can be observed in 30% of all cases and have been described after 13 years of initial diagnosis, which justifies the extended follow-up of these patients.J Med Cases. 2014;5(10):538-540doi: http://dx.doi.org/10.14740/jmc1933w