Within the space of several months, 2 very large randomized trials of screening for lung cancer have reported their findings, which fortunately complement one another. The National Lung Screening Trial (NLST) found that annual low-dose computed tomography (CT) reduced lung cancer mortality by 20% relative to annual chest radiography.1 In this issue of JAMA, investigators from the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Randomized Trial report that annual screening chest radiography does not reduce lung cancer mortality relative to no screening.2 Should clinicians infer that screening with low-dose CT reduces lung cancer mortality by 20% relative to no screening? This editorial addresses that question and several other aspects of the PLCO trial.