Mortality improvements affect the cost of retirement income of pensioners. In this work, the author examined how demographic factors such as age, gender, income and retirement decisions contribute to mortality patterns of civil servants in Nigeria. A sample size of 796 federal civil servants who retired between 1974 and 2008 in Lagos metropolis was used for this purpose. Correlation and Chi-square tests were used to analyze the data generated. The result of the findings shows that male mortality is lower than female's at every stage of retirement but not significant. The study also revealed that there is no significant difference between life expectancy of those who retired earlier and those who retired later. It was also shown that there is strong relationship between retirement decisions and income as well as income and mortality. Based on these findings, the author concluded that the new pension reform in Nigeria is still very new for its long-term implications to be evidence. However, the results of this work will no doubt be of great value to policymakers, Pension Fund Administrators and the regulators of pension system in Nigeria.