Online educational interventions are increasingly developed for health professionals and students, although graduate and undergraduate medical curricula often contain limited information about how to assess and manage pain. This study reviews the literature on the effectiveness of pain-related online educational resources. Studies were identified through a search of Medline, PsychINFO, Web of Science, CINAHL, PubMed, Scopus, Cochrane Library, Google Scholar, and OpenGrey databases. Search terms included 3 concept blocks: (1) type of intervention-online education, computer-based, e-learning, web-based, and internet-based; (2) population-pediatrician, physician, nurse, psychologist, and medical; and (3) outcome-pain*. Thirty-two studies (13 randomised controlled trials, 5 nonrandomised controlled trials, and 14 single-group pre-post studies) were included. Ten provided data for inclusion in a series of between-groups meta-analyses. After intervention, participants receiving online instruction had significantly greater knowledge compared with those receiving training as usual/alternative training (Hedges' g = 0.80, 95% confidence interval [CI]: 0.12-1.49), and students had significantly greater skills compared with students receiving training as usual (g = 1.34, CI: 0.38-2.30). No significant differences were found for confidence/competence (g = 0.02, CI: -0.79 to 0.84) or attitudes/beliefs (g = 0.16, CI: -0.48 to 0.79). Although online educational resources show promise in improving learner knowledge, considerable heterogeneity exists between studies in quality, design, educational content, and outcomes. Furthermore, methodologically robust RCTs are required to establish the effectiveness of online educational interventions and a greater understanding of the key features of successful online resources, including cognitive interactivity. Few studies assessed health outcomes for patients, remaining a major priority for future investigations.