Background Focal therapy has been introduced for the treatment of localised prostate cancer (PCa). To provide the necessary data for consistent assessment, all focal therapy trials should be performed according to uniform, systematic pre- and post-treatment evaluation with well-defined end points and strict inclusion and exclusion criteria. Objective To obtain consensus on trial design for focal therapy in PCa. Design, setting, and participants A four-staged consensus project based on a modified Delphi process was conducted in which 48 experts in focal therapy of PCa participated. According to this formal consensus-building method, participants were asked to fill out an iterative sequence of questionnaires to collect data on trial design. Subsequently, a consensus meeting was held in which 13 panellists discussed acquired data, clarified the results, and defined the conclusions. Outcome measurements and statistical analysis A multidisciplinary board from oncologic centres worldwide reached consensus on patient selection, pretreatment assessment, evaluation of outcome, and follow-up. Results and limitations Inclusion criteria for candidates in focal therapy trials are patients with prostate-specific antigen <15 ng/ml, clinical stage T1c-T2a, Gleason score 3 + 3 or 3 + 4, life expectancy of >10 yr, and any prostate volume. The optimal biopsy strategy includes transrectal ultrasound-guided biopsies to be taken between 6 mo and 12 mo after treatment. The primary objective should be focal ablation of clinically significant disease with negative biopsies at 12 mo after treatment as the primary end point. Conclusions This consensus report provides a standard for designing a feasible focal therapy trial. Patient summary A variety of ablative technologies have been introduced and applied in a focal manner for the treatment of prostate cancer (PCa). In this consensus report, an international panel of experts in the field of PCa determined pre- and post-treatment work-up for focal therapy research.