The authors document the very complex process involved in identifying insanity defense pleas in eight states. Each state and each study county in each state required an individual approach. Most often, county court dockets were hand searched to identify those pleading insanity, although numerous other methodologies were used. The frequency and rate of insanity pleas and acquittals are presented for the study states as well as descriptive data on the characteristics of persons pleading and acquitted NGRI. Overall, the insanity defense was raised in one percent of all felony cases. Further, only 26 percent of those raising the insanity defense were actually acquitted NGRI. The necessity of obtaining data on insanity pleas to adequately understand and ultimately inform future directions of insanity defense research is discussed.