introduction: the analysis of the smile is an important step for the diagnosis, planning, treatment and prognosis of any dentistry treatment involved with aesthetic goals. the evaluation of intrinsic characteristics of the smile is a necessary procedure so that one can be able to perform consistently a orthodontic treatment, requiring, for this aim, recognize the components and factors which interfere in these characteristics. objective: the objective of this paper is to present the six horizontal lines of the smile and its importance for achieving desired results in orthodontic treatment. conclusion: the analysis of the six horizontal lines of the smile facilitates the understanding of intrinsic characteristics that interfere with oral aesthetics. furthermore, the harmonization of these lines brings to each professional a greater chance of success in those treatments that include cosmetic purposes.