To describe the Avodart after Radical Therapy for prostate cancer Study (ARTS), investigating the use of dutasteride (a dual 5 alpha-reductase inhibitor that suppresses intraprostatic dihydrotestosterone, reduces tumour volume and improves other markers of tumour regression in prostate cancer) to prevent or delay disease progression in patients with biochemical recurrence after therapy with curative intent. An increasing serum prostate-specific antigen (PSA) level after radical prostatectomy (RP) or radiotherapy (RT) is indicative of recurrent prostate cancer and typically pre-dates clinically detectable metastatic disease by several years. ARTS is an ongoing European multicentre trial in which patients are stratified by previous therapy (RP with or without salvage RT vs primary RT) and randomized to double-blind treatment with dutasteride 0.5 mg or placebo once daily for 2 years. Eligible patients will have a PSA doubling time (DT) of 3-24 months. Biochemical recurrence is defined as three increases in PSA level from the nadir, with each increase >= 4 weeks apart and each PSA level >= 0.2 ng/mL, and a final PSA level of >= 0.4 ng/mL (after RP) or >= 2 ng/mL (after primary RT). Study endpoints include time to PSA doubling, time to disease progression, treatment response (PSA decrease or an increase of <= 15% from baseline), changes in PSA and PSADT, and changes in anxiety (Memorial Anxiety Scale for Prostate Cancer). ARTS will be the first study to evaluate the effects of dutasteride on PSADT, disease progression and treatment response in patients with biochemical failure after RP or RT, and should help to elucidate the potential role of dual 5 alpha-reductase inhibition in prostate cancer.