Purpose : To assess the impact of high dose three-dimensional conformal radiotherapy (3D CRT) for prostate cancer on the sexual function-related quality of life patients and their partners. Methods and Materials : Sixty of 124 consecutive patients (median age 72.3 years) treated with 3D CRT for localized prostate cancer were surveyed and reported being potent to treatment. The answers to survey questions assessing the impact of quality of life related to sexual function from these 60 patients and their partners forms the basis for this retrospective analysis. Results : Following 3D CRT, 37 of 60 patients (62%) retained sexual function sufficient for intercourse. Intercourse at least once per month was reduced from 71 to 40%, whereas intercourse less than one per year increased from 12 to 35%. Following treatment, 25% of patients reported that the change in sexual dysfunction negatively affected their relationship or resulted in poor self-esteem. This outcome was associated with impotence following treatment ( p < 0.01). Patients who had partners and satisfactory sexual function appeared to be at a higher risk of having a negatively affected relationship or losing self-esteem if they become impotent ( p < 0.05). Partners of patients who reported a negatively affected relationship or loss of self-esteem appear to be less likely to return the survey instrument used ( p = 0.02). Conclusions : More work is needed to evaluate the impact of radiotherapy and other treatments on the quality of life patients and their partners to allow adequate informed consent to be given.