In an accompanying commentary, Colgrove indicates that McKeown's thesis-that dramatic reductions in mortality over the past 2 centuries were due to improved socioeconomic conditions rather than to medical or public health interventions-has been "overturned" and his theory "discredited." McKeown sought to explain a very prominent trend in population health and did so with a strong emphasis on the importance of basic social and economic conditions. If Colgrove is right about the McKeown thesis, social epidemiology is left with a gaping hole in its explanatory repertoire and a challenge to a cherished principle about the importance of social factors in health. We return to the trend McKeown focused upon-post-McKeown and post-Colgrove-to indicate how and why social conditions must continue to be seen as fundamental causes of disease.