  We present 1428 individual astrometric measurements of 256 Transneptunian
objects made with HST. The observations were collected over three years with
two instruments, the Wide Field Planetary Camera 2 and the Advanced Camera for
Surveys High Resolution Camera, as part of four HST programs. We briefly
describe the data and our analysis procedures. The submission of these
measurements to the Minor Planet Center increased the individual arc length of
objects by 1.83 days to 8.11 years. Of the 256 total objects, 62 (24.2%) had
arc length increases \ge 3 years. The arc length for 60 objects (23.4%) was
increased by a factor of two or greater.
