OBJECTIVE To compare the results in patients with unilateral cT3 prostate cancer treated with or with no neoadjuvant androgen-deprivation therapy (nADT), as nADT might have benefit in cT2 prostate cancer, but for cT3 tumours its use remains controversial, and it is unclear whether it can prevent or delay progression after surgery. PATIENTS AND METHODS Between 1987 and 2004, 235 patients were assessed as having unilateral cT3 disease by a digital rectal examination; before surgery, 200 patients were not treated with nADT and 35 were. The Kaplan-Meier method was used to calculate survival rates. RESULTS With no nADT the biochemical progression-free survival (PFS) was 59.5%, the clinical PFS was 95.9%, the cancer-specific survival (CSS) was 98.7%, and overall survival was 95.9% at 5 years. With nADT, the biochemical PFS was 43.4%, clinical PFS was 77.6%, CSS was 88.7%, and overall survival was 79.8% at 5 years. The positive surgical margin rate with no nADT and with nADT was 33.5% and 57.1%, respectively, and the respective mean cancer volume was 6.6 mL and 4.0 mL. CONCLUSION nADT can decrease tumour size but does not reduce the positive surgical margin rate, nor improve the survival rate in unilateral cT3a disease. Because of side-effects and treatment costs, we do not advise nADT in patients with unilateral cT3a prostate cancer.