American Housing Survey (AHS) data, and publications based on these data (such as the Worst Case Needs reports), have consistently shown a surprisingly high proportion of renters spending more than 50 percent (and in some cases more than 100 percent) of their income for housing. Analysts have often questioned how these high cost burdens could be possible. This research examines the demographic characteristics of renter households with high rent burdens, the extent to which high housing costs or low incomes cause burdens, the persistence of burdens, and the comparability of AHS estimates with other data sources. Although the AHS does show a somewhat higher incidence of high burdens, other U.S. Census Bureau surveys show similar results. Longitudinal analysis of the same households shows instability in the incidence of high burdens over time, from both the cost and income sides. Some evidence suggests that observed high burdens may be the result of measurement error. A surprising result of this research is that households with high burdens do not move out of their units more frequently than those with lower burdens.