Dark-field electron micrographs obtained from thin webs of ultra-high molecular weight polyethylene shish-kebab crystals grown at 106 and 112°C show a random distribution of crystal defects with a mean separation of about 30 nm. Thermal shrinkage of these crystals also indicates a random distribution of defects, but with a mean separation of ∼1 μm. However, shrinkage is only affected by defects equivalent to complete loss of crystalline order, whereas electron microscopy is affected by single dislocations. Thus the core consists of long, but finite, crystals containing many randomly distributed defects.