The PoGOLite balloon-borne experiment applies well-type phoswich detector technology tomeasurements of soft gamma-ray polarization in the 25 keV - 80 keV energy range. The polarization isdetermined using Compton scattering and photoelectric absorption in an array of 217 plastic scintillators.This sensitive volume is surrounded by a segmented bismuth germanate oxide (BGO) anticoincidenceshield, designed to reduce background from charged cosmic rays, primary and atmospheric gamma-rays,and atmospheric and instrumental neutrons. A total of 379 BGO crystals with three different geometriesare used, giving an overall mass of approximately 250 kg. Tests of the BGO crystals are described andthe overall design of the anticoincidence shield is reviewed.