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Diffusion-weighted imaging and fluorine-18-fluorodeoxyglucose PET are increasingly being recognized as feasible oncological techniques. The apparent diffusion coefficient (ADC) measured by diffusion-weighted imaging and the standardized uptake value (SUV) from fluorine-18-fluorodeoxyglucose PET have similar clinical applications. The aim of this study was to assess the correlation between these two parameters in various cancers.Several major databases were searched for eligible studies. The correlation coefficient (ρ) values were pooled in a random-effects model. Begg’s test was used to analyze the existence of publication bias and the sources of heterogeneity were explored in subgroup analyses on the basis of study design, diagnostic method, scanning modality, and tumor type.Thirty-five articles were accepted. The pooled ρ value of all of the accepted studies was −0.30 (95% confidence interval: −0.33 to −0.27), and notable heterogeneity was present (I2=69.4%, P<0.001), which indicated a relatively weak negative correlation. The pooled ρ values were −0.26, −0.33, −0.32, and −0.33 for the SUVmax/ADCmean, SUVmax/ADCmin, SUVmean/ADCmean, and SUVmean/ADCmin relationships, respectively. The study design and diagnostic method were potential sources of heterogeneity. Lung cancer showed a stronger correlation (ρ=−0.42) than head and neck cancer (ρ=−0.27), cervical cancer (ρ=−0.21), and breast cancer (ρ=−0.23). A Begg’s test indicated no significant publication bias among the accepted studies (P>0.05).The two functional parameters of ADC and SUV showed a very weak inverse correlation, which may contribute toward a sophisticated characterization of tumor biology. However, the findings require further validation with trials with large samples and different tumor types.