Since the use of prostate-specific antigen screening has become widespread, prostate cancer at clinical T4 stage has become rare. Most bladder invasion is actually detected on radical prostatectomy specimens as a microscopic bladder neck involvement (BNI). The 2002 TNM classification system classified prostate cancer with BNI within a unified pT4 category, and rendered it equivalent to invasion into pelvic wall musculature or external sphincter. This decision is controversial. Various series have studied the clinical relevance and the impact of BNI on prognosis. Our evidence-based review provides support to the assignment of BNI within the subset of pT3 stage, and suggests that further improvement of the actual TNM staging system should be considered. However, BNI remains strongly associated with adverse pathology and should be regarded as a factor that worsens the prognosis of the underlying tumor stage.