Incidentally discovered adrenal masses, also known as incidentalomas, are adrenal masses that are found during diagnostic imaging or post-mortem examinations for reasons other than adrenal disease. A common finding in humans, incidentalomas are increasingly being diagnosed in small animals. Discovering an incidentaloma can present a significant diagnostic and therapeutic challenge. This chapter will help the reader distinguish benign from malignant, and functional from non-functional, adrenal tumours. The chapter also explains the management of incidentalomas based on their functionality and signs of malignancy. The importance of regular monitoring and evaluation of tumour growth is emphasized.