Soft tissue augmentation is widely practised by a variety of different practitioners. A new classification of filler substances and procedures, taking into account long-term safety and reversibility of side effects, is proposed: i non-permanent and biodegradable, ii semi-permanent and biodegradable, iii permanent and reversible, iv permanent and non-reversible. Complications and adverse effects occur with all fillers and all filler procedures. Insufficient experience is an important contributory factor. Underreporting is probably common. Commonest are haematomas, ecchymoses, infections, papulopustular or acneiform lesions, non-hypersensitivity related swelling and oedema, erythema, changes in pigmentation, palpability of the implant and necrosis of overlying tissue. Specific therapeutic approaches for these complications and practical recommendations to minimize or avoid them are discussed. Hypersensitivity reactions and granuloma formation are the most distressing adverse effects. They can occur with most fillers. Mostly these hypersensitivity reactions are local granulomas but, rarely, generalized reactions also occur. Case reports of systemic reactions after injection of hyaluronic acid are documented. Treatments include steroids, minocycline and immunomodulatory agents, such as cyclosporin, tacrolimus and ascomycin. In selected cases, surgical procedures are necessary to elimirate granulomatous reactions. Implant migration and facial lipoatrophy are encountered with certain compounds. Extreme caution is therefore advocated before using permanent and non-reversible products for soft tissue augmentation. Those who use fillers need to be familiar with the complications of fillers and with the treatment of those complications.