Injectable poly-l-lactic acid (PLLA-SCA) increases extracellular matrix to improve skin quality. The hip dell is an underappreciated element of gluteal aesthetics. Adipose tissue has roles in aesthetics and skin functioning. To investigate the efficacy of PLLA-SCA treatment to induce adipogenesis and volumize the hip dell. This was a double-blinded, split-body trial of 15 women with hip dell volume deficits. Each subject was randomized to have 1 hip dell treated with 150 mg of PLLA-SCA while the contralateral hip dell received the equivalent volume of saline. Subjects received 3 treatments at 1-month intervals and were followed for 9 months. Assessments included physician global aesthetic improvement scale, ultrasonography, and histologic examination. Blinded investigators rated PLLA-SCA-treated hip dells as improved and much improved. The dermis and adipose layers increased in thickness by 26.1% and 27%. These measures, in addition to collagen and elastic fiber quality, were significantly improved compared with saline-treated hip dells, which did not change from baseline. Subject satisfaction was also significantly greater on the PLLA-SCA-treated side. No subject experienced significant adverse effects. Poly-l-lactic acid is a safe and effective method for durable volumization and aesthetic improvement of the hip dell. PLLA-SCA may promote adipogenesis and elastogenesis.