Although most primary bone tumors and soft tissue tumors arise around the knee joint, many patients with tumoral conditions attribute their symptoms to traumatic events. This may lead to misdiagnosis and mistakes in selection of therapeutic approach. Arthroscopy is the preferred method for diagnosis and treatment of knee joint disease, but even a minimally invasive procedure may have adverse consequences in the presence of an unsuspected neoplasm. Thus, evaluation of all patients who may benefit from knee arthroscopy requires a careful and systematic workup that consists of appropriate noninvasive imaging studies and thoughtful consideration regarding the need for magnetic resonance imaging. Arthroscopic biopsy and treatment are recommended for selected intra-articular tumors. In addition, arthroscopy is a useful adjunct during surgical treatment of patients with certain juxta-articular benign bone tumors. In this Current Concepts review, we consider the risks and benefits of arthroscopy in the presence of tumors about the knee joint.