To promote long-term care policies for older adults, accurate mapping of the often invisible and insufficiently recognized role of their informal caregivers is needed. This paper measures the prevalence of informal caregivers in the European population, illustrates current difficulties in gathering unequivocal information on this topic and deals with the scientific and policy implications of the problem. Using the European Health Interview Survey (EHIS), the European Quality of Life Survey (EQLS) and the Study on Health and Ageing in Europe (SHARE), the current difficulties in gathering unequivocal information on this topic are illustrated. In most countries, the share of informal caregivers varies, sometimes markedly, among the three surveys. As for the sex of caregivers, while confirming the well-known higher prevalence of caregivers among women than among men, large variations emerge across the three surveys in most countries in respect of the two sexes. The takeaway message of the paper is that it is urgent to promote international concerted action in gathering comprehensive informal caregiving information and/or exploring in greater depth the different intercultural understandings of informal care itself.