This chapter provides an in-depth overview of the complications related to non-absorbable fillers, specifically polymethylmethacrylate (PMMA) and liquid injectable silicone (LIS), which, despite their effectiveness, can lead to severe and sometimes irreversible adverse effects. This chapter discusses early and late complications, including vascular occlusion, infection, nodule and granuloma formation, as well as systemic manifestations such as hypercalcemia and renal failure. Emphasis is placed on the importance of correct technique, early diagnosis, appropriate classification of complications, and individualized treatment protocols. Clinical strategies include pharmacological management, imaging tools for diagnosis, surgical intervention, and multidisciplinary follow-up. This chapter is grounded in clinical experience and supported by literature, providing essential guidance for safe practice and complication management in aesthetic medicine.