Background <p>Multiparametric prostate MRI (mpMRI) is widely used for prostate cancer detection and local staging. Imaging features such as marked diffusion restriction, intense contrast enhancement, and apparent extraprostatic extension are typically associated with aggressive malignancy. However, inflammatory conditions may rarely mimic locally advanced prostate cancer, potentially leading to overstaging and inappropriate treatment.</p> Case presentation <p>A 49-year-old man presented with nonspecific lower urinary tract symptoms and a serum prostate-specific antigen level of 2.7 ng/mL. mpMRI revealed a large mass-like peripheral zone lesion with marked diffusion restriction, rapid early enhancement, and imaging features suggestive of extraprostatic extension, leading to a PI-RADS 5 assessment and suspicion of locally advanced prostate cancer. Despite aggressive imaging findings, systematic biopsy demonstrated chronic prostatitis without malignancy. Following antibiotic therapy, short-term follow-up mpMRI showed marked regression of the lesion with resolution of diffusion restriction and contrast enhancement, confirming an inflammatory etiology.</p> Conclusions <p>Aggressive chronic prostatitis may closely mimic locally advanced prostate cancer on mpMRI, including apparent extraprostatic extension. Recognition of this diagnostic pitfall and careful radiologic–clinical correlation are essential to avoid overstaging and unnecessary definitive treatment.</p>