The decline observed in the infant mortality in the county of São Paulo since 1950 was due exclusively to the late infant mortality since the neo-natal mortality underwent slight oscillations. From the lowest value of 60,2 per 1000 reached in 1961 it became 73,0 per 1000 in 1966. This increase until 1964 was due not only to a increase in the neo-natal mortality (10,6% related to the 1961 value) but also in a increase in the late infant mortality (13,2% related to the 1961 value). In order to found which was the responsible causes for this so unfavorable trend of the infant mortality in the last years, the AA. drew the conclusion that only the infective and parasitic diseases did not have their rate increased in this period, having the other causes underwent a increase which ranged from 2,5% to 87,5% related to the 1961 value.
