© 2015 The Cochrane Collaboration. Background: Biologics are used for the treatment of rheumatoid arthritis and many other conditions. While the efficacy of biologics has been established, there is uncertainty regarding the adverse effects of this treatment. Since important risks such as lymphomas, serious infections and tuberculosis (TB) reactivation may be more common to the biologics but occur in small numbers across the various indications, we planned to combine the results from biologics used in many conditions to obtain much needed risk estimates. Objectives: To compare the potential adverse effects of tumor necrosis factor inhibitor (adalimumab, certolizumab, etanercept, golimumab, infliximab), interleukin (IL)-1 antagonist (anakinra), IL-6 antagonist (tocilizumab), anti-CD28 (abatacept), and anti-B cell (rituximab) therapy in patients with any disease condition except human immunodeficiency disease (HIV/AIDS). Methods: Randomized controlled trials (RCTs), controlled clinical trials (CCTs) and open-label extension (OLE) studies that studied one of the nine biologics for use in any indication (with the exception of HIV/AIDS) and that reported our pre-specified adverse outcomes (serious adverse events (SAEs), withdrawals due to adverse events (AEs), total AEs, serious infections; specific AEs, namely, tuberculosis (TB) reactivation, lymphoma and congestive heart failure) were considered for inclusion. We searched The Cochrane Library, MEDLINE, and EMBASE (to January 2010). Identifying search results and data extraction were performed independently and in duplicate. For the network meta-analysis, we performed both Bayesian mixed-treatment comparison models and arm-based generalized linear mixed models. Main results: We included 160 RCTs with 48,676 participants and 46 extension studies with 11,954 participants. The median duration of RCTs was six months and 13 months for OLEs. Data were limited for TB reactivation, lymphoma, and congestive heart failure. Using standard dose, compared with control, biologics as a group were associated with a statistically significant higher rate of total AEs (odds ratio (OR) 1.28, 95% credible interval (CI) 1.09 to 1.50; number needed to treat to harm (NNTH) = 22, 95% confidence interval (CI) 14 to 60), withdrawals due to AEs (OR 1.47, 95% CI 1.20 to 1.86; NNTH = 26, 95% CI 15 to 58), serious infections (OR, 1.37, 95% CI 1.04 to 1.82, NNTH = 108 95% CI, 50 to 989) and TB reactivation (OR 4.68, 95% CI 1.18 to 18.60; NNTH = 681, 95% CI 143 to 14706). The rate of SAEs, lymphoma and congestive heart failure were not statistically significantly different between biologics and control treatment. Certolizumab pegol (OR 4.75, 95% CI 1.52 to 18.65; NNTH = 12, 95% CI 4 to 79) and anakinra (OR 4.05, 95% CI 1.22 to 16.84; NNTH = 14, 95% CI 4 to 181) were associated with a statistically significantly higher risk of serious infections compared with control treatment. Compared with control, certolizumab was associated with a statistically significantly higher risk of SAEs (as defined in included studies: OR 1.57, 95% CI 1.06 to 2.32; NNTH = 18, 95% CI 9 to 162). Infliximab was associated with a statistically significantly higher risk of total AEs OR 1.55, 95% CI 1.01 to 2.35; NNTH = 13, 95% CI 8 to 505) and withdrawals due to AEs compared with control (OR 2.34, 95% CI 1.40 to 4.14; NNTH = 10, 95% CI 5 to 30). The overall numbers were relatively small for indirect comparisons. Indirect comparisons revealed that certolizumab pegol was associated with a statistically significantly higher odds of serious infections compared with abatacept, adalimumab, etanercept, golimumab and rituximab; and anakinra was statistically significantly more likely than rituximab to be associated with serious infections. Certolizumab pegol was associated with a statistically significant higher odds of SAEs compared with adalimumab and abatacept. No statistically significant differences were noted between biologics in total AEs or withdrawals due to AEs in indirect comparisons. Authors' conclusions: Overall, in the short term biologics were associated with statistically significantly higher rates of serious infections, TB reactivation, total AEs and withdrawals due to AEs. Serious infections included opportunistic infections as well as bacterial infections in most studies. Some biologics had a statistically higher association with certain adverse outcomes compared with control, but there was no consistency across the outcomes so caution is needed in interpreting these results. There is a need for more research regarding the long-term safety of biologics and an urgent need for comparative safety reports of different biologics; preferably without industry involvement. National and international registries and other types of large databases are relevant sources for providing complementary evidence regarding the short- and longer-term safety of biologics.