Introduction CoreTherm (ProstaLund AB, Lund, Sweden) is an outpatient treatment option in men with lower urinary tract symptoms and catheter-dependent men with chronic urinary retention caused by benign prostatic obstruction (BPO). CoreTherm is high-energy transurethral microwave thermotherapy with feedback technique. Modern treatment with CoreTherm includes transurethral intraprostatic injections of mepivacaine and adrenaline via the Schelin Catheter (ProstaLund AB, Lund, Sweden) and is often referred to as the CoreTherm Concept. Objectives The aim of this study was to evaluate the short- and long-term retreatment risk in men with large prostates and BPO or chronic urinary retention, all primarily treated with CoreTherm. Material and Methods All men from the same geographical area with prostate volumes >= 80 ml treated 1999-2015 with CoreTherm and having BPO or were catheter-dependent due to chronic urinary retention, were included. End of study period was defined as December 31, 2019. Results We identified and evaluated 570 men treated with CoreTherm, where 12% (71 patients) were surgically retreated during the follow-up. Mean follow-up was 11 years, and maximum follow-up was 20 years. The long-term retreatment rate in our study was 23%. A majority of these could be retreated with CoreTherm or TURP, with only 3% requiring open surgery. Conclusion We conclude that CoreTherm is a suitable outpatient treatment option in patients with profoundly enlarged prostates, regardless of age, prostate size, and reason for treatment.