This study evaluated the influence of upper lip length on maxillary incisal exposure at the rest position and categorized these findings according to sex in a young population. The degree of lip mobility between the rest position and maximum smile were also quantified. A total of 120 subjects (60 men and 60 women) with a mean age of 26.5 years (range: 18 to 35 years) participated in this study. Standardized photographs were taken of each subject at the rest position and at maximum smile. The following factors were evaluated and quantified: upper lip length at the rest position (categorized as short or normal lip length), maxillary incisal exposure at the rest position, dentogingival exposure at maximum smile, and overall lip mobility. Data were analyzed using the independent t test at a significance level of α = .05. In both men and women, there were significant differences between the normal and short lip groups in the amount of maxillary incisal exposure at rest (P < .05) but not in the amount of dentogingival exposure or overall lip mobility (P > .05). At maximum smile, all groups exhibited an approximately 30% decrease in upper lip length compared to the rest position. While the amounts of incisal and dentogingival exposure at rest and maximum smile may be used to evaluate facial/smile esthetics, there is a wide range of esthetically acceptable values. (Am J Esthet Dent 2012;2:116–125.)