The results of high-resolution laterally resolved measurements of positron implantation and diffusion are presented. High-magnification (4400\ifmmode\times\else\texttimes\fi{}), transmission-mode positron-reemission-microscopic images of a compound sample, which inhibited positron implantation in a well-defined region, were taken for positron implantation energies ranging from 3 to 9 keV. The lateral spreading was determined by examining the positron emission intensity across the boundary of the implantation inhibiting region. The lateral spreading is typically observed to be at least 500 \AA{} larger than the 1850 \AA{} value calculated using standard implantation and diffusion models. Possible explanations for the discrepancy are discussed.