Objectives: The question-behavior effect (QBE) refers to whether asking people questions can result in changes in behavior. Such changes in behavior can lead to bias in trials. This study aims to update a systematic review of randomized controlled trials investigating the QBE, in light of several large preregistered studies being published. Study Design and Setting: A systematic search for newly published trials covered 2012 to July 2018. Eligible trials randomly allocated participants to measurement vs. non-measurement control conditions or to different forms of measurement. Studies that reported health-related behavior as outcomes were included. Results: Forty-three studies (33 studies from the original systematic review and 10 new studies) compared measurement vs. no measurement. An overall small effect was found using a random effect model: standardized mean difference = 0.06 (95% CI: 0.02–0.09), n = 104,388. Statistical heterogeneity was substantial (I2 = 54%). In an analysis restricted to studies with a low risk of bias, the QBE remained small but significant. There was positive evidence of publication bias. Conclusion: This update shows a small but significant QBE in trials with health-related outcomes but with considerable unexplained heterogeneity. Future trials with lower risk of bias are needed, with preregistered protocols and greater attention to blinding.