Neural network modeling for small datasets can be justified from a theoretical point of view according to some of Bartlett’s results showing that the generalization performance of a multilayer perceptron (MLP) depends more on the L1 norm of the weights between the hidden layer and the output layer rather than on the total number of weights. In this article we investigate some geometrical properties of MLPs and drawing on linear projection theory, we propose an equivalent number of degrees of freedom to be used in neural model selection criteria like the Akaike information criterion and the Bayes information criterion and in the unbiased estimation of the error variance. This measure proves to be much smaller than the total number of parameters of the network usually adopted, and it does not depend on the number of input variables. Moreover, this concept is compatible with Bartlett’s results and with similar ideas long associated with projection-based models and kernel models. Some numerical studies involving both real and simulated datasets are presented and discussed.