Recent attempts to explain the decline of public health in England and Wales after 1948 have suggested that services had developed steadily but haphazardly in the interwar period, and that the lack of an underlying philosophy left Medical Officers of Health and their empires vulnerable to a range of forces that included the decline of infectious disease, the rise of hospital medicine, the growth of general practice, and the increasing professionalism of social work. Yet the argument that public health practitioners lagged behind contemporary thinking on social work in the 1950s deserves closer examination, and this article uses the rise and decline of the concept of the ‘problem family’ to examine the changing relationship between the two professional groups. It traces the emergence of the concept of the ‘social problem group’ in the 1930s, and considers why and how Medical Officers of Health and the Eugenics Society took up the idea of the ‘problem family’ after the Second World War. It charts how the Ministry of Health encouraged local authorities to use home helps and health visitors to tackle the ‘problem family’, and contrasts this medical approach. with the casework methods developed by voluntary organizations and subsequently adopted by the social work profession. The article concludes that in revealing how Medical Officers of Health were out of touch with contemporary research and practice in social work, the issue of the ‘problem family’ helps to explain the decline of public health under the early National Health Service.