With increasing survival rates in pediatric oncology, reports of long-term side effects persisting decades after treatment are also rising. Clinically evident nephropathies occur in about 5.5% of survivors more than five years after therapy. Chemotherapeutic agents such as ifosfamide, cisplatin, and carboplatin, as well as kidney-directed treatments like radiation, surgery, or stem cell transplantation, increase this risk. Acute kidney injury has also been described in association with cyclophosphamide and high-dose methotrexate, which are used in the treatment of acute lymphoblastic leukemia (ALL). Studies show a high prevalence of albuminuria (around 14.5% of childhood cancer survivors), an early marker of kidney damage, while standard parameters like creatinine often become abnormal only at later stages. Leukemia survivors suffer from vascular late effects caused by persistent endothelial damage triggered by cancer therapies such as anthracyclines, cyclophosphamide, and asparaginase, which increase inflammation and thrombosis risk. These vascular changes may also contribute to kidney injury. ULM is a high-resolution ultrasound technique that uses microbubbles to visualize the microvasculature and resolve dynamic blood flow changes with a resolution beyond the diffraction limit. ULM is independent of kidney or liver function, has been applied in various organs, and was recently used for the first time to visualize glomeruli-the smallest functional units of the kidney-in humans. This method enables early detection of glomerular injury as a consequence of vascular damage, even before albuminuria appears, potentially allowing earlier adaptation of follow-up and initiation of treatment. This pilot project focuses on survivors of ALL, as they are the largest and best studied pediatric cancer patient group also regarding late effects and, therefore, a sufficient number of individuals can be expected for his monocentric approach. Vascular functional impairment of the kidney could be detected at an early stage and the follow-up structures and measures such as the early use of nephroprotective drugs could be adapted.