Objective: Psychosexual morbidity is common after prostate cancer treatment, however, long-term prospective research is limited. We report 5-year outcomes from a couples-based intervention in dyads with men treated for localised prostate cancer with surgery. Methods: A randomised controlled trial was conducted involving 189 heterosexual couples, where the man received a radical prostatectomy for prostate cancer. The trial groups were peer support vs. nurse counselling versus usual care. Primary outcomes were sexual adjustment, unmet sexual supportive care needs, masculine self-esteem, marital satisfaction, and utilisation of erectile aids at 2-, 3-, 4- and 5-year follow-up. Results: The effects of the interventions varied across the primary outcomes. Partners in the peer group had higher sexual adjustment than those in the usual care and nurses group at 2 and 3 years (P = 0.002-0.035). Men in usual care had lower unmet sexual supportive care needs than men in the peer and nurse groups (P = 0.001; P = 0.01) at 3 years. Women in usual care had lower sexual supportive care needs than women in the peer group at 2 and 3 years (P = 0.038; P = 0.001). Men in the peer and nurse group utilised sexual aids more than men in usual care; at 5 years 54% of usual care men versus 87% of men in peer support and 80% of men in the nurse group. Conclusion: Peer and nurse-administered psychosexual interventions have potential for increasing men's adherence to treatments for erectile dysfunction. Optimal effects may be achieved through an integrated approach applying these modes of support.