Missing data creates various problems in analyzing and processing data in databases. In this chapter, a method aimed at approximating missing data in a database that uses a combination of genetic algorithms and neural networks is introduced. The presented method uses genetic algorithms to minimize an error function derived from an auto-associative neural network. The Multi-Layer Perceptron (MLP) and Radial Basis Function (RBF) networks are employed to form an auto-associative network. An investigation is undertaken into using the method to predict missing data accurately as the number of missing cases within a single record increases. It is observed that there is no significant reduction in the accuracy of the results as the number of missing cases in a single record increases. It is also found that results obtained from using the MLP are better than from the RBF for the data used.