OBJECTIVE Funding of systematic reviews by drug and device companies and other financial conflicts of interest among authors may have an impact on how the reviews are conducted. The aim of this study was to investigate if financial conflicts of interest are associated with results, conclusions, and methodological quality of systematic reviews. DESIGN This is a Cochrane methodology review. We searched PubMed, EMBASE, and the Cochrane Methodology Register as well as the reference lists of included studies and Web of Science for studies citing the included studies. We included observational studies of any design that investigated samples of systematic reviews with and without industry funding or other financial conflicts of interest, published up to November 2016. For studies to be eligible, they had to investigate at least 1 of our outcomes: effect size estimates, statistically favorable results, favorable conclusions, and methodological quality. Two review authors independently extracted data and assessed risk of bias in relation to study inclusion, data extraction, and comparability of the investigated systematic reviews. We reported our findings on effect size estimates qualitatively. We calculated pooled risk ratios (RRs) with 95% confidence intervals for statistically favorable results, favorable conclusions, and methodological quality. RESULTS Nine observational studies with a total of 983 systematic reviews of drug studies and 15 systematic reviews of device studies were included. Effect size estimates and frequency of statistically favorable results were similar between systematic reviews with and without financial conflicts of interest (Table). Systematic reviews with financial conflicts of interest more often had favorable conclusions compared with systematic reviews without financial conflicts of interest (RR, 1.96; 95% CI, 1.23-3.13). CONCLUSIONS Systematic reviews with financial conflicts of interest related to drug and device companies more often have favorable conclusions and to some degree lower methodological quality compared with systematic reviews without financial conflicts of interest. It remains unclear whether financial conflicts of interest have an impact on the results.