High levels of lamb loss have implications for the sustainability of hill sheep enterprises. A questionnaire survey was used to estimate the viable, healthy, mark to wean lamb loss on 40 Scottish Highland farms in the 2011 to 2012 lambing season. An average loss overall of about one in twenty (animal level 6.6%; flock level 6.2%) masked the wider range. A more detailed study of five holdings using electronic identification tags produced higher estimates of about one in five (animal level 18.6%; flock level 8.4 – 25.8%). Reasons for such heavy losses need further investigation, as they represent not only an animal health and welfare challenge but may contribute to environmental and social issues too.