Radiomicrosphere treatment involves the intrahepatic arterial administration of (90)Y-resin or (90)Y-glass microspheres. The microspheres are biocompatible, but not biodegradable, and little to no (90)Y leaches from the microspheres. Without any bioelimination, the beta-dose delivery is generally confined to the liver. Although U.S. Nuclear Regulatory Commission requirements permit patients treated with these microspheres to be released without the need for dose determination or patient instructions, there are important radiation safety issues that need scientific clarification. We carefully evaluated the radiation exposure mechanisms, including the bremsstrahlung radiation doses to others, for a variety of lifestyle behaviors. Dose estimates were also made for several practical and theoretic situations involving the patient's gonads, an embryo or fetus, and a nursing infant. For the infant, we evaluated the potential beta-dose that might be introduced via breast milk ingestion. The bremsstrahlung component of the decay scheme of the pure beta-emitter (90)Y has traditionally been ignored in internal and external dose calculations. Because the production of in vivo bremsstrahlung with the high-energy pure beta-particle-emitting radionuclides used for therapeutic purposes is sufficient to permit external detection and imaging, we believe that the contribution of such radiation should be considered with regard to patient release; we therefore chose to evaluate this potential external radiation hazard. In all cases, the estimated doses were very small, indicating that no patient restrictions are required for radiation safety purposes after the release of a patient who has been treated with (90)Y-microspheres.