Increasing incidence rates of cutaneous malignancies, paralleling rising survival times of grafts and patients in organ transplant recipients, represents an escalating challenge for dermatologists worldwide. Especially, invasive squamous cell carcinomas (SCC) in immuno-compromised patients are characterized by significantly increased morbidity and mortality and characteristically outnumber basal cell carcinoma in this population. Effective management of actinic keratoses (AK) could help to prevent the further development of invasive SCC. Diclofenac in hyaluronic acid has previously shown to be an effective and well tolerated option for the treatment of AK in immuno-competent patients. However, its safety and efficacy in organ-transplant patients has not been evaluated in a controlled study so far. 32 organ transplant patients (kidney (+/- pancreas), liver, heart) screened at our specialized transplant dermatology outpatient clinic were found eligible and were randomized to either active treatment (24) or vehicle (8). Patients who had stable status of the transplanted graft in the 12 months prior to entering the study and >/= 3 AK lesions in a contiguous 50 cm2 area on the face, forehead, hands or balding scalp were eligible for inclusion in the study. Treatment of AK with 3% diclofenac in 2.5% hyaluronic acid or placebo twice daily was conducted over a total of 16 weeks, followed by a final evaluation 4 weeks after last application of the study drug. Biopsies were taken from the treated areas at the final visit to verify clinical clearance. Patients were assessed for safety variables that included adverse events, local skin reactions, laboratory results, dosage of immunosuppressive medication and indication of graft rejection. A 24 months follow up was conducted after the end of treatment. 87% (n = 28/32) of the patients completed the 16 week treatment phase and presented for final evaluation 4 weeks after end of treatment. In the diclofenac 3% gel treatment group, a complete clearance of AK lesions was achieved in 41% (9/22) compared to 0% (0/6) in the vehicle group. Side effects in most of the patients included a mild erythema and a mild to moderate swelling of the areas treated. No graft rejections or trends for a deterioration of graft function were detected. No meaningful trends were observed in laboratory results. In 55% of the previously cleared patients, new AK developed in the study area after an average of 9.3 months. None of these patients developed invasive SCC in the study area within 24 months of follow-up. This study demonstrated a greater lesion clearance rate of AKs in OTRs treated with diclofenac 3% gel than with vehicle. Despite recurrent AK in 55% of the previously cleared patients, the 24 month results showed no invasive SCC in this group. This study suggests that diclofenac 3% gel is not only an efficient and well tolerated treatment for multiple AKs in OTRs but also may prevent invasive SCC in these high-risk patients.