<b><i>Introduction:</i></b> The aim of the study was to investigate the value of prostate-specific antigen density (PSAD) and lesion diameter (LD) combination in prostate cancer (PCa) detection. <b><i>Methods:</i></b> 181 patients who were detected to have prostate imaging-reporting and data system (PI-RADS) 3 lesions in mpMRI and underwent prostate biopsies were included in the study. Demographic, clinical, and pathological data of all patients were evaluated. The patients were divided into four groups according to PSAD and LD status (PSAD <0.15 ng/mL/cc + LD <1 cm, PSAD <0.15 ng/mL/cc + LD ≥1 cm, PSAD ≥0.15 ng/mL/cc + LD <1 cm, and PSAD ≥0.15 ng/mL/cc + LD ≥1 cm). Diagnostic ability for PCa and clinical significant PCa (csPCa) was evaluated by PSAD and LD. <b><i>Results:</i></b> PSAD ≥0.15 ng/mL/cc (OR = 6; 95% Cl = 2.847–12.647; <i>p</i> < 0.001), LD ≥1 cm (OR = 7.341; 95% confidence interval [CI] = 2.91–18.52; <i>p</i> < 0.001), and combination of PSAD ≥0.15 ng/mL/cc and LD ≥1 cm (OR = 10.023; 95% CI = 4.32–23.252; <i>p</i> < 0.001) were associated with PCa detection rates. The most sensitivity, specificity, negative, and positive predictive values were found in PSAD ≥0.15 ng/mL/cc + LD ≥1 cm group for both PCa and csPCa detection (48.8%, 92%, 85.2%, and 65.6% for any PCa detection; 66.7%, 85.2%, 97.3%, and 24.2% for csPCa detection, respectively). <b><i>Conclusion:</i></b> The presence of PSAD ≥0.15 ng/mL/cc or LD ≥1 cm in mpMRI of patients with PI-RADS 3 lesions is associated significantly with the finding of PCa and particularly with the detection of csPCa.