BACKGROUND: Laser-assisted MAL-PDT has been reported to increase the effectiveness of conventional PDT. Nonetheless, clinical effects of this association when reducing MAL incubation time is poorly discussed. Furthermore, the association of acoustic pressure wave ultrasound with laser-assisted MAL-PDT with short incubation time for field cancerization had not been reported before. OBJECTIVES: To compare clinical effects of ablative fractional laser-assisted MAL-PDT associated with acoustic pressure wave ultrasound (IMPACT US) with 1-hour incubation time and conventional MAL-PDT for skin field cancerization on the forearms, as well as the impact on safety and tolerability. METHODS: Fifteen patients with 638 AK (grade I-III) with field cancerized-skin on the forearms were enrolled in this left-right trial. Two protocols were randomly chosen. One side was treated with conventional MAL-PDT, whereas the other with laser-assisted MAL-PDT associated with acoustic pressure wave ultrasound with 1-hour incubation time. Actinic keratoses were quantitively measured, and the other signs of sun-damaged skin, like pigmentation and texture, in field cancerized skin were qualitatively evaluated before and after six months. Side effects were assessed subjectively during the procedure and one week after. RESULTS: All patients completed the study. At six months after treatment, both protocols reduced the number of AK (72%; CO2 + PDT, and 65%; MAL-PDT). The difference between these two protocols was not statistically significant (p = 0.77). The improvement of pigmentation and texture of field cancerized skin was more significant on the side treated with laser-assisted MAL-PDT associated with acoustic pressure wave ultrasound. Both protocols were well tolerated and without significant difference in adverse events. CONCLUSION: Laser-assisted MAL-PDT using CO2 laser and acoustic pressure wave ultrasound with short incubation time of 1 h was as effective as conventional MAL-PDT for field-cancerized skin with actinic keratosis in forearms with better cosmetic outcome.