Injectable fillers have gained popularity in recent years due to their low cost and quick recovery time compared to surgical procedures. However, soft tissue volume replacement with injectable materials is still a challenging problem for plastic surgeons, and the search for a safe, long-lasting, and predictable material continues today. Several main issues must be considered when using an injectable material, including the biological properties of the material, the location of the treatment area, the appropriate depth of injection, and the volume of material used. Permanent and non-permanent fillers have been used for body and facial contouring for decades and the most commonly used are hyaluronic acid, polyalkylimide, polyacrylamide, liquid silicone, and polymethyl methacrylate (PMMA). Unfortunately, for decades some non-specialist physicians and unethical non-medical practitioners have used PMMA injections inappropriately, claiming benefits such as “biocompatibility,” “non-migration,” “low incidence of granulomas,” and “low cost,” exposing patients to the risk of serious complications. Cosmetic PMMA injections can cause various issues, such as injection site reactions, hypersensitivity and immune reactions, infections, migration, and foreign body granulomas. In addition, other adverse events such as late inflammatory reactions in soft tissue fillers have been reported following SARS-CoV-2 infection and vaccination, including erythematous lumps, edema, or foreign body granulomas. This chapter presents the physiopathology, clinical presentation, and treatment of improper injections of large amounts of PMMA that can induce foreign body granulomas leading to calcitriol-mediated hypercalcemia, hypercalciuria with generation of urolithiasis or nephrocalcinosis, and acute kidney injury and progressive chronic kidney disease.