We report on two cases of infiltrative renal tumor developing in two kidney transplant recipients from a single cadaveric donor source. Interestingly, while this is only the second case of a de novo renal allograft tumor, both were morphologically infiltrative. The fact that both tumors were infiltrative may be secondary to immunosuppression therapy. While computed tomography (CT) evaluation of suspected renal pathology provides excellent anatomical detail, renal transplant recipients are initially evaluated using ultrasound and renal scintigraphy to avoid contrast reagents which could further impair renal function, as well as to reduce the image procedure cost and the patient radiation dose. Unfortunately, infiltrative tumors may be isoechoic on ultrasound, providing a confusing or conflicting report when compared to scintigraphic findings. This case report is significant radiographically because the original neoplasm was initially detected using technetium-99m-labeled mercaptoacetyltriglycine (99mTc-MAG3) scintigraphy and was not appreciated by sonographic studies, even retrospectively. This case demonstrates the usefulness of 99mTc-MAG3 scintigraphy to follow-up evaluations of renal transplants by providing detailed anatomical information as well as functional analysis of the kidney.