Background: To enhance the efficacy of photodynamic therapy (PDT) for actinic keratosis (AKs), physical and chemical pre-treatments, such as calcipotriol (CAL) have been suggested. Objectives: To compare the long-term 12-month efficacy and safety between methylaminolevulinate (MAL)-PDT and prior application of topical CAL versus conventional MAL-PDT for AKs of the scalp. Materials & Methods: Twenty patients with multiple AKs on the scalp were randomized to receive conventional PDT on one side of the scalp and CAL-assisted PDT, in which CAL was applied daily for 15 days beforehand, on the other side. Patients were evaluated for AK clearance at three, six and 12 months thereafter. Results: All 20 patients completed the study. At three months, overall AK clearance was 92.07% and 82.04% for CAL-PDT and conventional PDT, respectively (p < 0.001). Similar results were found at six and 12 months: 92.07% and 81.69% (p < 0.001), and 90.69% and 77.46% (p < 0.001) for CAL-PDT and conventional PDT, respectively. Grade I AKs showed a similar response rate for both sides (p = 0.055) at three months and significant differences were obtained at six (p = 0.001) and 12 months (p < 0.001) for CAL-PDT and conventional PDT. Grade II AKs showed greater improvement on the CAL-PDT side (89.55% vs 62.90%) (p < 0.001) at three months. No difference was found at six and 12 months. Conclusion: CAL-PDT proved to be safe and more effective than conventional PDT for the treatment of AKs on the scalp after 12 months. CAL pre-treatment may have enhanced the efficacy of PDT for AK treatment, however, larger trials are needed to corroborate our findings.