This paper discusses the following key issues concerning human exposure to polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) emitted from modern municipal waste combustors (MWCs): (1) Are MWCs the major source of PCDD/PCDF input into the environment; (2) Are environmental concentrations around MWCs substantially elevated relative to background levels; and (3) Are MWCs the major source of human exposure to PCDDs and PCDFs. Current scientific evidence indicates that: (1) combustion sources in general (including steel mills, copper melting plants, motor vehicles, hospital incinerators, and MWCs) are major sources of PCDD/PCDF input in the environment; (2) environmental concentrations of PCDDs and PCDFs around operating MWCs are not substantially elevated; and (3) 99% of human exposure to PCDDs and PCDFs is from background environmental contamination, even for individuals living near a modern municipal waste combustor. 43 refs., 4 tabs.