Although injections with copolyamide fillers (Aquafilling/Los Deline and Aqualift/Activegel) are currently used widely for breast augmentation, many complications have been reported. A recent position statement by a Korean aesthetic/reconstructive breast surgery society indicated these fillers are the same as polyacrylamide gel (PAAG), which is widely prohibited due to complications. To test this statement, this retrospective cohort study examined the clinical complications after breast augmentation with copolyamide fillers. Nuclear magnetic resonance (NMR) analysis of copolymer and PAAG fillers was also conducted. Methods: All consecutive patients with concerns about or sequelae from copolyamide fillers who visited our hospital in 2018-2020 were identified. The injected formulation, complications, and intraoperative findings were recorded. Copolyamide fillers were compared with PAAG and 2 PAAG fillers (Amazingel and Aquamid) by NMR. Results: Of the 29 patients (all women; average age, 42 years), 17 complained of breast deformity. Eight had puncture site infections and mammary gland inflammation. Five exhibited induration (single large/small lumps). In 4 cases, the filler had migrated outside of the breast, including to the back and vulva; these cases had severe symptoms. NMR showed that the copolyamide and PAAG fillers bore all of the characteristic peaks of PAAG. Conclusions: Our clinical/intraoperative and NMR findings showed, respectively, that copolyamide fillers cause the same complications as PAAG fillers and have the same composition. Thus, the risks of copolyamide fillers for breast augmentation are equivalent to those for PAAG fillers. It is strongly recommended not to use copolyamide fillers until their long-term safety is established.