Backround-Complex renal cysts and masses occur in all age groups, right from WiIm’s tumor that commonly occurs in children, renal cell carcinoma (RCC) in adults; to the rarer multilocular cystic nephroma (MLCN), which is found in both the age groups, although with different sex predilections. Objectives- To evaluate imaging characteristic of complex renal cysts and the role of USG (including Doppler) and CECT. Methods- The study was conducted on 42 patients in the Radiology department of Command Hospital Air Force, Bangalore from December 2014 to July 2016. Cases were included in the study after taking informed consent. All patients were examined by CECT and USG (including Colour Doppler) whenever required. USG studies were performed using real time equipment utilizing 3.5 MHz curvilinear electronic probes and Colour Doppler, whenever required. In paediatric patients, 7.5 MHz linear electronic probes were used. CT examinations were performed using an MDCT scanner (Volume Zoom; Philips, Somatom AR-HP I Somatom HiQ systems Forcheim, Germany) with a gantry rotation of 0.5 seconds. SPSS was used for analysis. Results- there are 42 patients in our study, who on CT scan were seen to have cystic renal lesions of them, 33 (79%) patients were adults, with the oldest of our patients being 85 years old (mean age -40.3 years). 21(42%) were predominantly cystic masses and 28 (58%) were predominantly solid. Of the predominantly cystic masses 10 (20%) were unilocular cysts and 11 (22%) were multilocular cysts. we had 10 (20%) cases with unilocular cystic renal lesions. We excluded simple cysts less than 3 cm in diameter. Amongst these 10 patients with unilocular masses, 1(10%) patients had renal cell carcinomas and 9 (90%) had simple renal cysts (including complex benign cysts). Malignancy was seen in 1 patient, which though comprising only 10% of unilocular lesions is a significant number. Conclusion- a suspected renal mass should undergo a USG as the first line of imaging. A confident diagnosis of simple cyst should make one stop from further imaging.