It has long been recognized that both localized and metastatic renal cell carcinoma (RCC) can exhibit great clinical heterogeneity in terms of growth and progression. The natural history of small renal masses (SRMs) managed by active surveillance (AS) has provided an excellent model to characterize these tumours by renal tumour biopsy (RTB) to both rule out non-malignant mimics and to better understand histologic subtype natural history and correlates with genomics and other markers that might have clinical utility. We measured the growth kinetics and progression patterns of RCC SRMs (SRMRCC) from the largest cohort of biopsy characterized SRM patients on AS. A multicenter Canadian prospective trial cohort was combined with our Princess Margaret cohort to serially measure tumour size in 136 biopsy proven RCCs in 134 patients presenting with SRMs managed by AS. There was wide variation in the growth and progression rates between the different histological subtypes of SRMRCC and between histologically similar cc SRMRCC. Characterizing the histology of SRM may allow individualized treatment recommendations for patients including AS for the remaining life of older and/or infirm patients.