Biomonitoring Equivalents (BEs) are defined as the concentration or range of concentrations of a chemical or its metabolite in a biological medium (blood, urine, or other medium) that is consistent with an existing health-based exposure guideline such as a reference dose (RfD) or tolerable daily intake (TDI). BE values can be used as a screening tool for the evaluation of population-based biomonitoring data in the context of existing risk assessments. This study reviews health based risk assessments and exposure guidance values for 2,2',4,4',5-pentabromodiphenylether (PBDE-99) from Health Canada and the United States Environmental Protection Agency (US EPA). Toxicokinetic data from laboratory animals and humans are reviewed. A BE value corresponding to the US EPA RfD is derived here for PBDE-99 based on the assumption of chronic steady-state exposure, distribution into body lipids, and a previously-estimated first-order half-life of elimination of 1040days. The steady-state lipid-adjusted BE(RfD) is 520ng/g lipid. Sources of uncertainty relating to the underlying toxicokinetic and toxicologic database for PBDE-99 and the simultaneous exposure to multiple PBDE congeners are discussed. The BE(RfD) value may be used as a screening tool for evaluation of population biomonitoring data for PBDE-99 in the context of the existing US EPA risk assessment and can assist in prioritization of the potential need for additional risk assessment efforts for PBDE-99 relative to other chemicals.