Small renal masses <4 cm are most often incidentally discovered on cross-sectional imaging for unrelated indications and pose a unique clinical dilemma for evaluation and management. While ~80% of these prove malignant upon resection or biopsy, the majority demonstrate indolent behavior, growing slowly and rarely metastasizing. Differentiating between aggressive and indolent pathologies remains a diagnostic challenge, even with modern imaging and biopsy techniques. Active surveillance has emerged as an alternative to primary intervention in appropriately selected patients, with the intent of estimating adverse pathology risk through longitudinal monitoring of tumor behavior before making the decision to treat. Long-term data are now available, showing that this is a safe initial management option for patients with small renal masses.