Background: Aesthetic soft-tissue filler injections for lip enhancement are popular and performed throughout the world. When injecting lips with a cannula, as the cannula is advanced, resistance is perceived in consistent locations, potentially indicating boundaries between intralabial compartments. Objective: We aimed to investigate whether intralabial compartments exist and, if so, to describe their volumes, location, boundaries, and dimensions. Methods: This cadaveric study investigated a total of 20 human body donors (13 male, seven female) with a mean (SD) age at death of 61.9 years (23.9) and body mass index of 24.3 kg/m2 (3.7). The investigated cohort included 11 White donors, eight Asian donors, and one Black donor. Dye injections simulating minimally invasive lip treatments were conducted. Results: Independent of sex or race, six anterior and six posterior compartments in the upper and lower lip were identified, for a total of 24 lip compartments. Compartment boundaries were formed by vertically oriented septations that were found in consistent locations. The anterior compartments had volumes ranging from 0.30 to 0.39 cc; the posterior compartment volume ranged from 0.44 to 0.52 cc. The compartment volumes were larger centrally and decreased gradually toward the oral commissure. Conclusions: The volume and size of each of 24 compartments contribute to the overall appearance and shape of the lips. To achieve a natural lip shape preserving aesthetic outcome it may be preferable to administer the volumizing product using a compartment-respecting injection approach.