OBJECTIVE: To analyse the impact of the presence of extra-target non-clinically significant cancer (NCSC) after high-intensity focused ultrasound (HIFU) hemiablation on oncological results. To analyse radical treatment free survival (RTFS) rates at 2-3 years follow-up. METHODS: Retrospective single-centre study of 55 patients treated by primary HIFU hemiablation from 2010 to 2016. Inclusion criteria were unilateral MRI detected CSC, stage ≤ T2b, Gleason score (GS) ≤ 7, at least 6 mm distant from prostate apex. MRI with systematic and targeted biopsies was performed at diagnosis. Follow-up included clinical examination, PSA every 6 month, MRI and biopsies at 1 year and in case of PSA elevation. HIFU retreatment was possible. Whole-gland treatment was indicated in case of positive biopsies with GS ≥ 7 or maximum cancer core length > 5 mm, any GS. RESULTS: Mean follow-up was 33 months (SD: 17-49 months). Presence or not of an extra-target NCSC in the untreated part of the gland had no impact on RTFS at univariate analysis (p = 0.29). 10 (18%) patients had a salvage whole-gland treatment after a median follow-up of 26 months (IQR 17-28). RTFS at 2 and 3 years were 92% and 80%. CONCLUSIONS: Presence or not of an extra-target NCSC in the untreated part of the gland had no impact on RTFS. NCSC lesion can be left untreated and actively monitored. RTFS was 80% at 3 years which support the concept of focal/partial treatment as a treatment option of CSC prostate cancer.