Résumé : Our objective was to obtain practical clinical parameters to indicate those actinic keratoses (AK) that are at risk of becoming invasive. A systematic review of the literature, with focus on randomized trials, retrospective studies and reviews was undertaken. The main outcome measure was the rates and clinical features of AK that transformed into SCC. This study reviewed randomized and retrospective studies and reviews of AK and their risk of becoming SCC. We reviewed a total of 875 studies and identified 62 useful prospective, retrospective studies and reviews. Finally 15 studies covering percentage and/or clinical parameters of malignant transformation were found to be useful: a total of 9 reviews, 4 randomized controlled trials and 2 retrospective studies. Only 1 study (meta-analysis) examined the percentage of malignant transformation and found a rate between 0.025% and 20% per year/per lesion. Clinical parameters found were: induration (3 studies), bleeding (3 studies), enlargement in diameter (3 studies), erythema (2 studies) and ulceration (2 studies). Other minor clinical criteria were pain, palpability, hyperkeratoses, pruritic lesions and pigmentation. The amount of quality research on the most common premalignant lesion in humans is disappointing. The only longitudinal study looking at the incidence of malignant transformation of AK to SCC dates from 1988.Besides the known risk factors (skin type, photodamage, immunosuppression etc), based on this review we found clinical features that provide a practical guide to practitioners in the treatment of AK. Although not prospectively studied, clinical parameters indicating those AK with an increased risk of malignancy are IDRBEU. I (Induration /Inflammation), D (Diameter > 1 cm), R (Rapid Enlargement), B (Bleeding), E (Erythema) and U (Ulceration). In future prospective studies, these parameters should be included.