A comparative study was performed to examine the nature of the gingival smile line (GSL), a specific dentolabial configuration characterized by the exposure of maxillary anterior gingiva during a full smile. Five soft-tissue, three dental and three skeletal variables were selected, measured and reported for a GSL sample (n = 27) and a reference sample (n = 88), both consisting of North American white orthodontic patients with a median age of 14.4 years. The results indicated that the capacity to project a gingival smile was related to: anterior vertical maxillary excess and the muscular ability to raise the upper lip significantly higher than average when smiling. Other variables significantly associated with GSL were greater overjet, greater interlabial gap at rest, and greater overbite. Factors that did not appear associated with the GSL phenomenon were upper-lip length, incisor clinical crown height, mandibular plane angle, and palatal plane angle. Clinical aspects of GSL were discussed.