Earthworm populations and their casting/burrowing activities were recorded in rotations on paired organic and conventional farms. Earthworm abundance was often higher in organic systems, the proportion of ley being a key influence. Casting (surface) and burrowing (surface and 30 cm depth) were related to population indices and these relationships compared between the two systems. Surface casting was common only during ley phases. Surface casting and burrowing were often more abundant in organic rotations but in many cases deep burrowing was greater in conventional rotations. These differences were only partly explained by population data. There was some indication that surface activity was greater in organic rotations even when population differences were discounted. Differences in behaviour between rotation phases and systems may have implications for soil function.