BACKGROUND: Men with negative prostate biopsies or those diagnosed with low-risk or low-volume intermediate-risk prostate cancers often require a second prostate biopsy prior to a treatment decision. Prostate HistoScanning (PHS) is an ultrasound imaging test that might inform prostate biopsy in such men. METHODS: PICTURE was a prospective, paired-cohort validating trial to assess the diagnostic accuracy of imaging in men requiring a further biopsy (clinicaltrials.gov, NCT01492270) (11 January 2012-29 January 2014). We enrolled 330 men who had undergone a prior TRUS biopsy but where diagnostic uncertainty remained. All eligible men underwent PHS and transperineal template prostate mapping (TTPM) biopsy (reference standard). Men were blinded to the imaging results until after undergoing TTPM biopsies. We primarily assessed the ability of PHS to rule out clinically significant prostate (negative predictive value [NPV] and sensitivity) for a target histological condition of Gleason ≥4+3 and/or a cancer core length (MCCL) ≥6 mm. We also assessed the role of visually estimated PHS-targeted biopsies. RESULTS: Of the 330 men enrolled, 249 underwent both PHS and TTPM biopsy. Mean (SD) age was 62 (7) years, median (IQR) PSA 6.8 (4.98-9.50) ng/ml, median (IQR) number of previous biopsies 1 (1-2) and mean (SD) gland size 37 (15.5) ml. One hundred and forty six (59%) had no clinically significant cancer. PHS classified 174 (70%) as suspicious. Sensitivity was 70.3% (95% CI 59.8-79.5) and NPV 41.3% (95% CI 27.0-56.8). Specificity and positive predictive value (PPV) were 14.7% (95% CI 9.1-22.0) and 36.8% (95% CI 29.6-44.4), respectively. In all, 213/220 had PHS suspicious areas targeted with targeting sensitivity 13.6% (95% CI 7.3-22.6), specificity 97.6% (95% CI 93.1-99.5), NPV 61.6% (95% CI 54.5-68.4) and PPV 80.0% (95% CI 51.9-95.7). CONCLUSIONS: PHS is not a useful test in men seeking risk stratification following initial prostate biopsy.