There is a historical dilemma concerning the civil rights of psychiatric patients who are believed to need a protected status because of incompetency. California's Lanterman -Petris-Short Act provides a mechanism for putting the patient under the care of a conservator if the patient is unable to provide for his own personal needs of food, clothing, and shelter. If successful, this legislation will likely be the model for the country.Fifty-one patients for whom the clinical staff desired to initiate conservatorship proceedings were given a test consisting of behavioral tasks specifically designed to be appropriate to the legal definition of grave disability. The natural groupings were: chronic organic brain syndrome, chronic schizophrenia, and other.We found that the grave disability of the organic brain syndrome patients was fairly predictable from their mental status examination, while the grave disability of the chronic schizophrenic patients was unpredictable from their mental status examination and required the application of the behavioral test for an appropriate determination of their ability to perform the functions specified in the law: The Lanterman Petris-Short Act to provide for personal needs of food, clothing, and shelter. When the method or the proceedings were applied to patients of other diagnostic categories, they were found to be inappropriate.At this writing, our method of evaluation is being recognized and requested by public and legal agencies in our area. It has been used as evidence in court. The procedure is clear, relevant, and easily taught to new workers. The results, given in plain English and in essay form, are readily understood by physician, social worker, judge, and jury alike. We began our study with vexation, ambiguous criteria, and a chronic medical and legal problem; we conclude with a practical and relevant answer.