To date, the existing literature on the natural history, growth, and progression patterns of small renal masses (SRMs) has not been informed by a histology-specific approach. In addition, we know that up to 30% of SRMs are not renal cell carcinoma (RCC), thus study cohorts have been heterogeneous and do not reflect RCC subtype malignant tumor behavior alone. We thus aimed to report histology-specific growth and progression in the largest cohort of biopsy-confirmed SRM (RCC) managed by initial active surveillance (AS).