The goals were to assess risk factors and mortality rate changes over time and to develop simple estimates of mortality rates for specific groups of infants at 23 to 26 weeks of gestation. Data from the Israel national very low birth weight infant database on 3768 infants born in 1995-2006 with gestational ages (GAs) of 23 to 26 weeks were evaluated, and we developed a tool for estimating infants' mortality rates. Major factors associated with death were GA, gender-specific birth weight percentile, prenatal steroid therapy, and multiple births. There was a steady decrease in mortality rates for all GAs during the study period. In 2004-2006, mortality rates before discharge were 89%, 67%, 46%, and 26% for infants with GAs of 23, 24, 25, and 26 weeks, respectively. Estimated mortality rates were calculated as the sum of the percentages determined for each of 4 parameters, as follows: GA of 26, 25, 24, or 23 weeks, 0%, 17%, 34%, and 51%, respectively (P < .001); birth weight percentile of >75th, 25th to 75th, or <25th, 0%, 16%, and 32%, respectively (P < .001); no prenatal steroid treatment, +22% (P < .001); multiple birth, +7% (P = .1). Estimated mortality rates for the 48 subgroups of infants ranged from 0% to 100% and correlated well with observed rates (intraclass correlation coefficient: 0.89). Mortality rates for infants born at 23 to 26 weeks of gestation could be estimated simply on the basis of GA, gender-specific birth weight quartiles, prenatal corticosteroid therapy, and multiple births.