Patient description: The patient is a 63-year-old man presenting to the Emergency Department with a history of acute urinary retention in the past 2 days. Abdominopelvic CT scan revealed a large prostate and a bladder filled with urine. He is a candidate for urethral catheterization and TURP. Further evaluation revealed: Post-void residual: 71 mL Prostate volume (TRUS): 63 mL Prostate-specific antigen (PSA) level: 3.5 ng/mL His recent blood chemistry (3 days ago) was normal: Hgb: 13.6 g/dl WBC: 133000 /mm3 Plt: 370000 /ml PT: 12 second PTT: 34 second INR: 0.9 Creatinine: 0.5 mg/dl BUN: 10 mg/dl U/A: Color: yellow Appearance: cloudy PH: 5.3 Specific gravity: 1.010 Glc: 100 Nitrite: negative Ketone: none Leukocyte esterase: negative RBC: negative WBC: 2 WBCs/hpf U/C: negative

Clinical trial eligibility criteria: eligible ages (years): 50.0-999.0,  Benign Prostatic Hyperplasia (BPH) Diagnosis of BPH and eligible for endoscopic BPH surgery including Transurethral Resection of the Prostate [TURP], PVP, electrovaporization 2. Prostate volumes 30 gm based on transrectal ultrasound 3. Men ≥ 50 years of age 4. IPSS symptom score > 15 and IPSS bother score > 2 5. Baseline peak flow rate Qmax < 12 cc/s on two separate occasions with voided volume at least 150 cc  History of prostate or bladder cancer, pelvic radiation, untreated bladder stones, urethral strictures/bladder neck contracture (BNC), renal insufficiency (i.e. creatinine > 1.4) 2. Neurogenic bladder, Parkinson's disease 3. Prior treatment for urinary incontinence 4. Micturition frequency AND urgency. Micturition frequency defined as > 8 micturitions per 24 hours as assessed by a thorough subject history including the question: "On average, how many times do you void during a 24 hour period? // < 4, 5-7, 8 or more." Urgency defined as an uncontrollable urge to void that occurs > 3 per 24 hours as assessed through the subject history/question: "On average, how many times a day do you have an uncontrollable urgency to void? // 0, 1-2, 3 or more?" 5. Intravesical prostate lobe protrusion > 1 cm on TRUS. Note: this is distinct from lateral lobes protruding up to the bladder such as an intravesical protrusion without median lobe 6. Active Urinary Tract Infection [UTI] (i.e. must have a screening urinalysis without signs of infection or a negative urine culture) 7. PVR > 250 at time of enrollment or catheter dependent bladder drainage 8. History of chronic prostatitis within the last 5 years 9. Not able to temporarily discontinue aspirin, Coumadin, Plavix and any other anticoagulant at least seven days prior to the time of treatment 10. History of known bleeding disorders (e.g. von Willebrand disease) 11. Prior BPH prostate procedures (e.g. Transurethral Microwave Therapy [TUMT], TUNA, water induced thermotherapy, TURP, PVP) 12. Men with confirmed or suspected malignancy of the prostate based on a digital rectal exam (DRE), prostate biopsy or PSA > 10 ng/mL. Men with free PSA < 25% and with PSA within an age and race-specific range may only be enrolled after a negative biopsy. If a biopsy is required, the subject shall have a six-week waiting period between the biopsy and histotripsy treatment, if he is deemed eligible to participate in the study. 13. Men interested in future fertility 14. Declines or unable to provide informed consent 15. Non-English-speaker 16. Life expectancy estimated to be less than one year 17. Unable or unwilling to complete all required questionnaires and follow-up assessments 18. In the opinion of the investigator, it is not in the subject's best interest to participate in the study