Purpose ASCO provisional clinical opinions (PCOs) offer direction to the ASCO membership after publication or presentation of potential practice-changing data. This PCO addresses second-line hormonal therapy for chemotherapy-naïve men with castration-resistant prostate cancer (CRPC) who range from being asymptomatic with only biochemical evidence of CRPC to having documented metastases but minimal symptoms. Clinical Context The treatment goal for CRPC is palliation. Despite resistance to initial androgen deprivation therapy, most men respond to second-line hormonal therapies. However, guidelines have neither addressed second-line hormonal therapy for nonmetastatic CRPC nor provided specific guidance with regard to the chemotherapy-naïve population. Recent Data Six phase III randomized controlled trials and expert consensus opinion inform this PCO. Provisional Clinical Opinion For men with CRPC, a castrate state should be maintained indefinitely. Second-line hormonal therapy (eg, antiandrogens, CYP17 inhibitors) may be considered in patients with nonmetastatic CRPC at high risk for metastatic disease (rapid prostate-specific antigen doubling time or velocity) but otherwise is not suggested. In patients with radiographic evidence of metastases and minimal symptoms, enzalutamide or abiraterone plus prednisone should be offered after discussion with patients about potential harms, benefits, costs, and patient preferences. Radium-223 and sipuleucel-T also are options. No evidence provides guidance about the optimal order of hormonal therapies for CRPC beyond second-line treatment. Prostate-specific antigen testing every 4 to 6 months is reasonable for men without metastases. Routine radiographic restaging generally is not suggested but can be considered for patients at risk for metastases or who exhibit symptoms or other evidence of progression. Additional information is available at www.asco.org/genitourinary-cancer-guidelines and www.asco.org/guidelineswiki .