Purpose: This study aimed to investigate late urinary incontinence (UI) after salvage radiotherapy (sRT) and the effect of dose escalation on late UI, incontinence recovery, and quality of life (QoL) as part of the SAKK 09/10 phase III trial. Methods: The SAKK 09/10 trial was a multicenter, randomized, controlled trial for prostate cancer patients receiving sRT. Eligible patients were randomized to receive either conventional (64 Gy) or dose-escalated (70 Gy) sRT. Baseline and follow-up data were collected on urinary incontinence related QoL, and treatment toxicity. Results: 344 evaluable patients were analyzed. Baseline incontinence (≥Grade (G)1) was reported in 32.2 % of patients, with 8.7 % having ≥ G2. During follow-up (median 6.2 years), 47.2 % of the initially continent (<G1) patients showed a statistically significant (p < 0.001) decline in continence with no significant difference between the treatment groups (p = 0.17). Of the initially incontinent patients, 54.1 % showed an improvement whilst 16.2 % showed further decline. 29.7 % had stable UI. There was no significant difference between the treatment arms (p = 0.36). In multivariable logistic regression, nerve sparing technique was associated with less UI at 24 months (p = 0.029) and at 60 months age (p = 0.031) and resection status (p = 0.046) were significant. There was a steady worsening of urinary symptoms reported over 60 months post RT, with an increase in the symptom scales from a mean of 15.9 at baseline to 22.9 at 60 months. Conclusion: More than half of the patients that were continent at baseline remained continent during follow up while incontinent patients showed a variable course. UI was not different between the RT treatment arms.