Hydronephrosis (HDN) is the most common radiological anomaly seen on prenatal scans. With the universal availability of prenatal sonography, most of these cases are detected antenatally. Subsequent presentation in the post-natal period is incidental, or with symptoms of pain, lump, or urinary tract infection. While the causes for dilatation can be many, not all are obstructive. It is therefore important to identify the etiology and further evaluate for the requirement of surgery in these patients. The outcomes are dependent upon the underlying etiology. The cystic diseases of kidney include muticystic dysplastic kidney (MCDK), cystic neoplastic disease and several other cystic diseases with genetic association.