To investigate the impact of Prostate Imaging Quality (PI-QUAL) scores on the diagnostic performance of multiparametric MRI (mpMRI) in a targeted biopsy cohort. 300 patients who underwent both mpMRI and biopsy were included. PI-QUAL scores were retrospectively assigned by two radiologists in consensus and were correlated to pre-biopsy PI-RADS scores and biopsy outcomes. Clinically significant prostate cancer (csPCa) was defined as ISUP grade ≥ 2. Image quality was optimal (PI-QUAL ≥ 4) in 249/300 (83%) and suboptimal (PI-QUAL < 4) in 51/300 (17%). The proportion of PI-RADS 3 scores referred for biopsy was higher in scans of suboptimal vs optimal quality (51% vs 33%). For PI-QUAL < 4 scans, the positive predictive value (PPV) was lower compared to PI-QUAL ≥ 4 (35% 95%CI: 22, 48 vs 48% 95%CI: 41, 55; difference −13% 95%CI: −27, 2; p 0.090), as was the detection rate of csPCa in both PI-RADS 3 and PI-RADS 4–5 (15% vs 23% and 56 vs 63%, respectively). The overall MRI quality increased over time. Scan quality may affect the diagnostic performance of prostate mpMRI in patients undergoing MRI-guided biopsy. Scans of suboptimal quality (PI-QUAL < 4) were associated with lower PPV for csPCa.