BACKGROUND: Contrast-enhanced computed tomography (CT) and magnetic resonance (MR) imaging for lymph node (LN) staging of prostate cancer (PCa) are largely inadequate. OBJECTIVE: Our aim was to assess prospectively the sensitivity, specificity, and positive and negative predictive values for the LN staging by (11)C-choline positron emission tomography (PET)-CT and MR diffusion-weighted imaging (DWI) of the pelvis before retropubic radical prostatectomy (RRP) with extended pelvic LN dissection (PLND). DESIGN, SETTING, AND PARTICIPANTS: From February 2008 to August 2009, 36 patients with histologically proven PCa and no pelvic LN involvement on contrast-enhanced CT with a risk >/= 10% but </= 35% at LN metastasis according to the Partin tables were enrolled in this study. INTERVENTION: Patients preoperatively underwent (11)C-choline PET-CT and DWI. Subsequently all patients underwent a wide RRP and an extended PLND. MEASUREMENTS: Sensitivity, specificity, and positive and negative predictive values (PPV and NPV) for LN status of (11)C-choline PET-CT and DWI were calculated with the final histopathology of the LNs as comparator. RESULTS AND LIMITATIONS: Seventeen patients (47%) had a pN1 stage, and 38 positive LNs were identified. On a LN region-based analysis, sensitivity, specificity, PPV, NPV, and the number of correctly recognised cases at (11)C-choline PET-CT were 9.4%, 99.7%, 75.0%, 91.0%, and 7.9%, respectively, and at DWI these numbers were 18.8%, 97.6%, 46.2%, 91.7%, and 15.8%, respectively. Twelve LN regions containing macrometastases, of which 2 had capsular penetration, were not detected by (11)C-choline PET-CT; 11 LNs, of which 2 had capsular penetration, were not detected by DWI. This is a small study with 36 patients, but we intend to recruit more patients. CONCLUSIONS: From this prospective histopathology-based evaluation of (11)C-choline PET-CT and DWI for LN staging in high-risk PCa patients, it is concluded that these techniques cannot be recommended at present to detect occult LN metastases before initial treatment.