Dairy cattle spend, on average, between 8 and 15 h/d lying down. The objective of this experiment was to describe the laterality of lying behaviour and assess several internal and external factors that may affect laterality. Internal factors included time spent and time since eating or lying before choosing to lie down again. External factors included the slope and the amount of bedding on the lying surface. Laterality in lying is shifted to the left in some groups but not others. Eating behaviour has little effect on overall time spent lying on either side. Cows switch sides on 64% of consecutive lying bouts and the likelihood of switching increases if the previous bout has been either recent or long. Probably, continuous lying may become uncomfortable when bouts are longer than 80 min, and cows may switch sides to alleviate this discomfort.