A renal transplant is a surgically implanted donor kidney, typically placed in the iliac fossa (lower pelvis) and connected to the patient’s iliac vessels and bladder. Ultrasound is the primary imaging modality for post-transplant surveillance because the transplanted kidney is superficially located and easily accessible to sonographic evaluation. Sonographers assess the transplant for size, echogenicity, and hydronephrosis, and Doppler evaluation of the renal artery, renal vein, and intrarenal arteries is performed to check for vascular complications such as renal artery stenosis, renal vein thrombosis, and arteriovenous fistula. The resistive index in the transplant’s intrarenal arteries is monitored — elevated values may suggest rejection, though this finding is non-specific. Peritransplant fluid collections (hematoma, lymphocele, abscess) are also identified and monitored by ultrasound.