Exploiting the link between land identification and farm accountancy data, we use a uniquely detailed database to conduct a robust analysis of land fragmentation and its effect on technical inefficiency on dairy farms in Ireland. Using a stochastic production frontier model, our results show that the number of parcels, the average distance between parcels and the main farm, and the portion of land separate from the main farm all increase technical inefficiency. Such inefficiency can be reduced through increased parcel area, reduced travel distances, advisory services contact, intensive practices and hired labour. Our findings support the need for policy to improve land and labour mobility, providing evidence to support incentives to promote the transfer and long-term leasing of agricultural land.