Ultrasound is the most important non-invasive diagnostic tool for detecting morphological pathological alterations of the kidneys. With a low patient burden it permits rapid, potentially serial and highly reproducible bed-side diagnoses of postrenal acute kidney injury and chronic kidney disease. Within chronic kidney disease, polycystic kidney disease can reliably be detected and evidence can be obtained for ischemic nephropathy, diabetic nephropathy and chronic pyelonephritis by renal size and intrarenal morphological alterations. An additional domain of ultrasound is the differentiation of the dignity of solid and cystic renal lesions. Newly introduced contrast-enhanced ultrasound is of additional help as benign and malignant lesions display different perfusion patterns. Renal artery stenosis can reliably be identified and its hemodynamic effect can be assessed with a combination of direct and indirect criteria by Doppler and duplex ultrasound.