Objective: To study the safety, efficacy, optimal volume, and longevity of an injectable hyaluronic acid (HA) gel dermal filler to treat facial temporal fossa fat loss. Methods and materials: This open-label, single-site, 12-month study used 20 mg/mL HA gel to correct volume loss in both temples in 30 subjects. Touch-ups were allowed at week 2. At each visit, the investigator completed a Frontal Temporal Fossa Scale and a 7-point satisfaction scale. Subjects completed a 7-point satisfaction scale, Subject Global Aesthetic Improvement Scale (GAIS), and self-perception of age assessment. Photos were taken at each visit. Results: Subjects who returned for the one-month visit (29) achieved a ≥ 1-point improvement on the Temporal Fossa Scale in both temples. At month 12, 98% of the temples maintained a ≥ 1-grade, 18% showed a 3-grade, 34% showed a 2-grade, and 46% showed a 1-grade improvement. All subjects received an average of 1.1 mL per temple. Mild to moderate jaw pain after injections was noted by 40% of patients. The pain was reported to occur during mastication. There was no correlation between the amount of the study device injected and the incidence of jaw pain, which did not occur at the touch-up injections and was self-limited. Injections were well tolerated, and no patients developed vascular compromise, vascular events, or visual disturbances. Conclusion: HA gel (20 mg/mL) is safe and efficacious when used in the facial temporal fossa. The results lasted at least 12 months in 98% of subjects. Most subjects perceived themselves as looking younger than at baseline. J Drugs Dermatol. 2019;18(1):67-74.