['This is a prospective study of psychiatric patients presenting to the emergency department (ED) to determine the value of routine laboratory studies used to attempt to exclude concomitant medical illness.', 'Physical exams and laboratory tests were performed on 375 psychiatric patients presenting for "medical clearance" in the ED. Upon completion of these tests, the percentage and impact of abnormal physical exams and laboratory results were assessed.', 'Fifty-six of 375 patients (14.9%) had a non-substance-induced laboratory abnormality. Forty-two of these 56 patients (75.0%) also had abnormal history or physical exam findings indicating laboratory screening. Ten had normal history and physical exams with insignificant laboratory abnormalities. The four (1.1% [95% CI 0.3-2.7%]) remaining patients with normal history and physical exams had abnormal urinalyses which did not affect final disposition or contribute to altered behavior.'] Is routine laboratory testing to evaluate for medical illness in psychiatric patients in the emergency department largely unrevealing?