Kaposi's sarcoma (KS) is a rare complication of renal transplantation in Poland (in our center 2 of 1000 patients). Neovascularization (typical for KS) is promoted by KS-related vascular endothelial growth factor (t-r-VEGF). Sirolimus may reduce t-r-VEGF synthesis and inhibit PI3K-p70S6 kinase of endothelial cells. Two men, 58 and 51 years old, were transplanted in 2002. Initial immunosuppression consisted of cyclosporine, azathioprine, and prednisone. In the second patient, at the week 8 the immunosuppression was switched to tacrolimus and mycophenolate mophetil. KS symptoms appeared on hard palate and skin in month 7 in both patients. In the first patient, the X-ray showed enlargement of mediastinal lymph nodes and diffuse interstitial infiltrates with nodular changes in both lungs. Serum creatinine of the first patient was increased from 1.6 to 1.9 mg/dL, while in the second it remained stable (approximately 2.0 mg/dL). Since confirmation of KS immunosuppression has been minimized in both patients; all drugs except prednisone were withdrawn, and sirolimus was introduced (1-2 mg/24 hours blood level 5-8 ng/mL). Within a month the progression of lung and skin disease ceased, and patients' conditions began to improve with lung opacities regressing, the biggest skin lesions diminishing and smaller ones disappearing. Within 1 year renal function improved. Our observation suggests that sirolimus-based immunosuppression proffers the possibility of KS regression with concomitant renal function preservation among renal graft recipients. It is difficult to ascertain whether KS regression may be attributed to sirolimus treatment or to the reduced overall immunosuppression.