In this issue of AJKD, Eriksson et al1 analyze data from a Finnish longitudinal birth cohort study of more than 20,000 individuals born from 1924 to 1944 and followed up from birth to death. The study was prompted by the rapidly evolving discipline of the developmental origins of health and disease, established by the seminal observations of Barker and Osmond,2 who discovered a correlation between low birth weight and cardiovascular disease in adults. Barry Brenner et al3 subsequently proposed a similar relationship between low nephron number at birth and adult hypertension.