Polyethylene glycol (PEG) performs multiple roles for bone tissue engineering scaffolds. Successful in vivo implantation for long periods of time requires a scaffold that is biocompatible, osteoconductive, osteoinductive, and promotes cell recruitment and attachment. PEG has significant advantages such as excellent biocompatibility and flexibility, but certain drawbacks such as poor mechanical strength and cell attachment limit its use as a plain scaffold. Instead, it is often used as an additive, composite, or delivery system. Below is a summary of current research involving the use of PEG-based biomaterials in bone tissue engineering, specifically with regard to long term in vivo effects.