BACKGROUND: One of the goals of lip augmentation is to recreate the natural shape and contour of the lips. The literature describes numerous fillers and multiple techniques for this procedure. However, there is a paucity of information regarding the anatomy of the fat layers of the upper and lower lips. While prosecting cadavers, the authors noted the presence of fat deep to the orbicularis muscle of the lip and a separate fat compartment deep to the mentalis muscle. This anatomy has not been previously described. METHODS: The authors dissected a total of 10 cadaver specimens. Dissection of the upper and lower lips and chin was performed. Latex injection of the arterial circuit aided the identification of boundaries. Histologic examination was performed on full-thickness specimens using hematoxylin and eosin stains. RESULTS: Fat was noted deep to the orbicularis oris and mentalis muscles. This fat is distinct from the more superficial fat of the cutaneous lip. The wet-dry border of the lip appears to be the most anterior boundary of the submuscular lip fat. The lateral boundary is the zygomaticus muscle. Histologic examination confirms this macroscopic anatomy. CONCLUSIONS: If volume loss is a significant component of facial aging, it becomes important for the clinician to know the precise anatomy of the subcutaneous tissue. Greater precision is possible in rejuvenating specific characteristics of aging. Augmentation at the vermilion cutaneous junction defines the vermilion border and improves perioral rhytides. Deep fat augmentation of the vermilion restores volume, shape, and lip eversion. Augmentation of submuscular fat beneath the cutaneous lip improves the convex shape. Submentalis fat augmentation specifically reduces the depth of the labiomental hollow. These findings are in agreement with previous observations that volume loss of deep fat-temporal, buccal, and sub-orbicularis oculi fat -contributes to the aging process. Knowledge of this anatomy and site-specific augmentation make it possible for the clinician to approach perioral rejuvenation in an algorithmic fashion.