Collateral adverse outcomes are the expected or unavoidable results of a procedure that is performed in a standard manner and typically experienced by the patient. Collateral adverse outcomes do not result from errors, nor are they rare. Collateral adverse outcomes occur as the direct result of a surgical procedure and must be accepted as a trade-off to attain the intended benefits of the surgical procedure. As such, collateral adverse outcomes do not fit into the traditional definition of a complication or adverse event. Examples of collateral adverse outcomes after lumbar spine arthrodesis include lumbar stiffness, postoperative psychological stress, postoperative pain, peri-incisional numbness, paraspinal muscle denervation, and adjacent-level degeneration. Ideally, a comparison of interventions for the treatment of a clinical condition should include information on both the negative consequences (expected and unexpected) and potential benefits of the treatment options. The objective evaluation and reporting of collateral adverse outcomes will provide surgeons with a more complete picture of invasive interventions and, thus, the improved ability to assess alternative treatment options.