This study utilized existing blood-lead surveillance data and records of housing properties treated for lead hazard control (LHC) in order to investigate the effectiveness of LHC treatments performed in four Massachusetts communities (Boston, Cambridge, Malden, and Springfield). This research is part of the US Department of Housing and Urban Development's (HUD) overall program evaluation strategy for assessing the effectiveness of their LHC Grant Program. Childhood blood-lead levels (BLLs) in housing units that were treated through HUD's LHC Grant Program were compared to BLLs in untreated matched control housing units. Data from multiple sources-local housing departments, local tax assessor departments, and the Massachusetts Department of Public Health-were linked to identify similar sets of treated and untreated dwellings. Geometric mean BLLs from before and after treatment were compared for the two sets of housing. Ten years of blood-lead surveillance data for children living in the selected dwellings were analyzed using log-linear mixed models and logistic regression models. Results indicate a 50% decline in BLLs in treated homes, a significantly larger decline than in untreated homes after adjusting for the general downward trend in BLLs observed in the general population for the last several years. Data show that homes that received HUD LHC treatments had children with blood-lead levels that declined twice as fast as in similar untreated homes. These findings show that LHC efforts are successful in reducing children's blood-lead levels.