The objective of this research was to investigate the variability of base layer construction in hot-mix asphalt (HMA) pavements and to assess the impact of base layer variability or nonuniformity on pavement performance. Subjective acceptance criteria of base layer construction may lead to variable pavement performance and may result in early pavement distresses and failure. Eleven existing HMA pavement projects with aggregate base course layers constructed in the past few years were selected for falling weight deflectometer (FWD) testing and visual distress surveys. In six of these projects, Issues with aggregate base performance (stability and uniformity) had been observed und reported during paving of the HMA surface layer. Later, these pavements exhibited various levels of early distresses. Including cracking (longitudinal, transverse, and alligator), aggregate base failure, and pavement surface roughness or Irregularities (for ride quality). The remaining five HMA pavement projects, for which no Issues related to aggregate base layer behavior were reported during construction, performed well after construction. A test section of approximately 1 mi on each project was subjected to FWD testing. The existing HMA pavements that showed early distresses exhibited high levels of spatial variability und nonuniformity in aggregate base course layers, as demonstrated by FWD testing and backcalculated base layer modulas values and distributions. The existing HMA pavements that performed well exhibited low levels of spatial variability und good uniformity in aggregate base course layers, as shown by the FWD test results und the backcalculated base layer modulus values and distributions.