Objective: To evaluate the association and discriminatory performance of diffusion MRI-derived apparent diffusion coefficient (ADC) values for ¹⁸F-FDOPA PET-defined metabolic activity in newly diagnosed glioma. Methods: This was a retrospective study of 87 treatment-naïve adults, who were initially evaluated for newly diagnosed or radiologically suspected glioma at Baghdad Teaching Hospital, Medical City, Baghdad from January 2026 to July 2026. Pretreatment diffusion MRI and ¹⁸F-FDOPA PET/CT results were evaluated. PET activity was determined a priori as TBRmax ≥1.60 as an approximated operational application of PET RANO 1.0. The mean ADC was compared across PET groups, associated with SUVmax and TBRmax and assessed by ROC analysis. WHO grade analyses were done in 80 individuals with histological confirmation. Results: Forty-six tumors were PET-active and 41 were PET-inactive. Mean ADC was lower in PET-active tumors (1.04 ± 0.24 vs 1.16 ± 0.23 ×10⁻³ mm²/s; p=0.029), whereas SUVmax was higher (3.73 ± 0.98 vs 2.06 ± 0.45; p<0.001). ADC correlated inversely with TBRmax (Spearman rho=−0.32; p=0.003) and SUVmax (rho=−0.29; p=0.006). The AUC was 0.62 (95% CI, 0.50–0.74). At ADC ≤1.20 ×10⁻³ mm²/s, sensitivity was 84.8%, specificity 41.5%, and accuracy 64.4%. Conclusion: ADC was moderately inversely correlated with 18F-FDOPA uptake but was poor in discriminative ability alone. The lower bound of the AUC confidence interval was near chance performance. The cutoff from this cohort is experimental and should not be used for guiding clinical choices without external confirmation.