Organ transplant recipients (OTRs) are at high risk of developing cutaneous squamous cell carcinoma (SCC); prevention includes early treatment of premalignant actinic keratosis (AK). Photodynamic therapy (PDT) is a noninvasive field therapy that reduces new AKs in patients with existing AK and delays SCC development in mice. We investigated the effect of repeated PDT over 5 years for primary prophylaxis of skin dysplasia. These data represent an interim analysis of an on-going randomized controlled trial. During 2008-2011, 25 renal transplant recipients with clinically normal skin were randomized to split-side PDT of the face, forearm and hand, the contralateral side serving as untreated control. Patients received PDT on inclusion and at 6-monthly intervals for 5 years. Blinded evaluation was performed at each visit. We found that prophylactic PDT significantly delayed onset of AK compared with untreated skin, p = 0.020. At 3-year follow-up, we observed AK in 63% of patients in untreated skin areas compared with 28% of patients in PDT-treated skin, with a total number of cumulated AKs in untreated skin (n = 43) compared with PDT-treated skin (n = 8), p = 0.005. These preliminary data indicate a novel approach to early prevention of skin dysplasia that may reduce morbidity from multiple AKs and SCCs in OTR.