Given the growing use of dermal fillers for cosmetic lip augmentation, a validated instrument with which to measure lip fullness is desirable in the clinic and as an efficacy endpoint in clinical studies. The authors developed and conducted a validation study of a Medicis-developed lip fullness scale. The Medicis Lip Fullness Scale consists of separate five-point scales for the upper and lower lips, with three photographs exemplifying each grade. Five board-certified dermatologists or plastic surgeons assessed 85 test photographs for each lip on two separate occasions for the first round of validation (photograph versus photograph). Three of the evaluators also graded lip fullness in 39 live subjects, followed 2 weeks later by scoring of the same subjects' photographs for the second round of validation (live versus photographic). Within-observer agreement between the two sequential photographic evaluations was almost perfect (weighted κ = 0.81). Between-observer weighted κ values ranged from 0.60 to 0.83 for the upper lip and 0.61 to 0.82 for the lower lip. Exact agreement between the live and photographic assessments of the same subjects was 60 percent and 52 percent for upper and lower lips, respectively. The Medicis Lip Fullness Scale showed high interrater and intrarater reliability in comparisons of test photographs and moderate to substantial reliability in live assessment of patients versus photographs. The Medicis Lip Fullness Scale is suitable for grading lip fullness in clinical trials. Diagnostic, III.