Wada testing has been a standard part of temporal lobectomy evaluation since the early 1960s. Although the procedure was initially used to lateralize language function, it was soon modified to assess risk for postoperative amnesia. The use of the procedure has now evolved to include prediction of degrees of memory decline. This use has been criticized, but more recent research has better described important parameters of the procedure and supported its validity. The Wada test is effective in lateralizing seizure onset, predicting postoperative seizure control, and predicting degree of verbal memory decline following left temporal lobectomy. The validity of Wada test data has also been supported by correlations between Wada memory performance and hippocampal pyramidal cell loss or MR imaging determined hippocampal volumes. It remains to be seen, however, if Wada memory performance and data from other sources such as MR imaging, ictal SPECT, positron emission tomography, or functional MR imaging are redundant or independently contribute to patient diagnosis and management.