Incidence rates for the first year of life are separated into two pieces (1–6 months and 6–12 months). This separation was possible by utilizing the complete enumeration of the Olmsted County population. The incidence rates for 1–6 months were 159.6 for boys, and 117.2 for girls, and 138.8 overall cases per 100,000 persons per year‥ Similarly, the rates for 6–12 months were 80.6 for boys, 93.3 for girls, and 86.8 overall cases per 100,000 persons per year. For comparability with other studies and to allow for age- and sex- adjustment to the U.S. population, the incidence rates for the complete first year of life are reported as one age category in Table 3.