Renal transplantation is the preferred treatment of patients suffering from end stage renal disease. Because of challenges in performing surgical vascular anastomosis in variant renal anatomy, knowledge on renal vascular anatomy is very important in the pre surgical workup of potential kidney donors. These anatomical variations differ geographically and ethnically. In Kenya there has been scanty statistics on prevalence of extra-renal branching of arteries but also the clear knowledge in the understanding of the relation between renal sizes, their main arterial diameters in predicting the presence of accessory arteries without invasive diagnostic methods. This study was designed to add into the body of literature more information about the dimensions of renal vascular anatomy of adult African population in Kenya and transmit this knowledge to enrich the renal surgery practice in the region and beyond. Therefore the aim of this study was to determining the relationship between kidney size, main renal arterial caliber and how they relate in the presence or absence of accessory arteries. The study was a three-year crosssectional descriptive study conducted at Kenyatta National Hospital from June 2008 to June 2011. A total of 204 cases including 103 (50.5%) females and 101 (49.5%) males were recruited for CTA. Most normal sized kidneys with accessory arteries had smaller main renal arterial diameters. Extra renal branching occurred in 14.7% of cases. It is concluded that the presence of accessory arteries cannot be determined by the study of kidney sizes alone. The current value of Renal CTA cannot be easily replaced by simplified noninvasive modalities for indirect and accurate study of renal vascular anatomy of potential kidney donors.