Background: Five-year results from the CHHiP trial indicated that moderate hypofractionation of 60 Gray (Gy)/20 fractions (f) was non-inferior to 74Gy/37f (Lancet Oncology, 2016). Reporting of long-term efficacy and side effects is essential in a patient population that remain at risk of recurrence years after treatment. Here we report specific co-morbidity data collected at 10 years and an update of efficacy. Methods: Between October 2002 and June 2011, 3216 men with node negative T1b-T3a localised prostate cancer with risk of seminal vesical involvement ≤30% were randomised (1:1:1 ratio) to 74Gy/37f (control), 60Gy/20f or 57Gy/19f. Patients received 3-6 months of androgen deprivation prior to radiotherapy. The primary endpoint was time to biochemical failure (Phoenix consensus guidelines) or clinical failure (BCF). The non-inferiority design specified a critical hazard ratio (HR) of 1.208 for each hypofractionated schedule compared to control. Data on specific radiotherapy related co-morbidities were collected at 10-year follow-up and are presented as frequency and percentages. Analysis was by intention-to-treat; HRs quoted are unadjusted. Results: With a median follow up of 12.1 years, 10-year BCF-free rates (95% CI) were 74Gy: 76.0% (73.1%, 78.6%); 60Gy: 79.8% (77.1%, 82.3%) and 57Gy: 73.4% (70.5%, 76.1%). For 60Gy/20f, non-inferiority was confirmed: HR₆₀=0.84 (90% CI 0.72, 0.97) with borderline significance for superiority (HR=0.84 (95% CI 0.70, 1.00). As in the primary analysis, for 57Gy/19f, non-inferiority could not be declared: HR₅₇=1.13 (90% CI 0.98, 1.30). 10-year overall survival (95% CI) was 78.5% (75.9%, 81.0%), 82.9% (80.4%, 85.0%) and 79.9% (77.3%, 82.2%) in the 74Gy, 60Gy and 57Gy groups. Bone fractures were reported in 2% (15/700), 2% (19/771) and 3% (22/719) of patients in the 74Gy, 60Gy and 57Gy groups respectively at 10 years. The most common intervention reported was a sigmoidoscopy with 12% (79/681), 8% (60/739) and 9% (65/702) in the 74Gy, 60Gy and 57Gy groups respectively. Of those patients who underwent a sigmoidoscopy it was due to symptoms for 81% (63/78) 81% (48/59) and 85% (55/65) of patients in the 74Gy, 60Gy and 57Gy group respectively. Frequencies of all other pre-specified co-morbidities or related interventions (ureteric obstruction, bowel strictures, trans-urethral resection of prostate, urethrotomy, urethral dilatation or long term catheterisation or treatment of proctopathy with steroid, sucralfate, formalin, laser coagulation or rectal diversion) were <1% in all groups. Conclusions: With a median follow-up of 12 years, oncological outcomes following 60Gy/20f continue to be non-inferior to those with 74Gy/37f. Late co-morbidities were very low across all treatment groups. These data support the long-term safety of moderate hypofractionation. Clinical trial information: 97182923.