The hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), is not a serious pest of hemlocks in China, but it has caused alarming mortality of hemlocks in Northeast America. Understanding to what degree hemlocks are infested with HWA in China should shed light on an ongoing investigation of natural enemies of HWA in China for the potential of biological control of HWA in North-America. Our objectives were to know whether the HWA occurrence differed among cardinal directions, between crown heights, between generations (over time), or among sites.  We studied HWA in three different sites (each with 10 randomly selected trees) in Lijiang Prefecture, Yunnan Province, from August 2005 to December 2006, in reference to different environmental factors. Within a tree (each with 400 1-year foliage branches), HWA occurred at higher percentages in thenorth and southfacing directions; HWA infestation was usually more severe atthe lower crown than the upper, but it was reversed in May when higher percentages of HWA were found on the upper crown of a tree. This seasonal difference in infestation between crown heights coincided with the onset of the new HWA generation. The infestation rate of 1-year foliage branches with HWA averaged 24.6% over the three sites, where Heyuan had higher HWA infestation than Maoniuping or Heishuihe.  A correlation analysis with 12 plots (each with 10 randomly selected trees) from the three sites indicated that aspect (slope orientation), average annual relative humidity, and average annual rainfall were positively correlated with the infestation rate of HWA at significant statistical levels, while temperature, altitude, slope degree, canopy closure, and tree height seemed to have little effect on HWA occurrence.  Search for natural enemies should consider more efforts on the north and southfacing directions of a tree and at lower crown height where HWA tend to be denser.