OBJECTIVE To investigate the efficacy of low-dose flutamide (125 mg twice daily) in the treatment of prostate-specific antigen (PSA) recurrence after definitive treatment with radical retropubic prostatectomy (RRP), external-beam radiation therapy (RT), or cryotherapy. METHODS In this phase II prospective trial, patients who had a PSA recurrence after definitive treatment for prostate cancer were treated with flutamide. Endpoints for assessing treatment efficacy were PSA progression, treatment toxicity and clinical symptoms. Results were stratified into complete response (PSA < 0.2 ng/mL on two consecutive assessments), partial response (PSA decrease of half that at baseline on two consecutive assessments) and progressive disease. Seventeen patients were enrolled in who definitive treatment for primary prostate cancer had failed. RESULTS Low-dose flutamide was clinically effective (i.e. complete or partial response) in 13 patients. Four had a complete response (mean duration 28 months), nine a partial response (mean duration 19 months), and two progressive disease, but were in the study for a mean of 1 year before progression. Two patients discontinued the study at 3 months, secondary to drug-related toxicity; one had grade 3 toxicity and five grade 1 toxicity. CONCLUSIONS The administration of low-dose flutamide (125 mg) was clinically effective in treating PSA recurrence after definitive treatments for prostate cancer, and was well tolerated. Further investigation in a phase III trial is warranted.