One third of individuals aged \>60 years will be diagnosed with at least one renal cyst following abdominal imaging. These cystic lesions are categorized according to the Bosniak classification which categorizes cysts according to their degree of complexity and risk of malignancy. Growing evidence suggests that a significant proportion of Bosniak III and IV cysts are benign and that the malignant ones present low metastatic potential. Since renal surgery carries substantial morbidity (20%) and potential mortality (0.5%), active surveillance has gained attention as a potential tradeoff to surgery to overcome overtreatment. Therefore, prospective studies of long-term follow-up are needed to confirm the oncologic safety of this strategy for patients with Bosniak III/IV cysts. This is an multicenter prospective observational longitudinal study. The main objective is to compare the 5-year follow-up cancer-specific survival between the active surveillance and the surgical groups.