As general hospitals search for ways to cut costs without sacrificing efficiency, particular attention has been focused on factors that may prolong hospital stay. The results of prior studies that have reported an association between psychological and psychiatric comorbidity and longer hospital stays have been subject to different interpretations because of methodological design flaws. The current paper reports on a study of psychological comorbidity and length of stay that has been designed to avoid the methodological problems of earlier investigations. The study was performed at a 429-bed tertiary-care, university-affiliated, voluntary, teaching hospital. During hospital days 3 to 5, patients were tested as available with the Mini-Mental State examination, the Zung Depression Inventory, and the SCL-90 and were rated for physical impairment with the Karnofsky Performance Status Scale. Statistical analyses were performed for correlations between length of stay and test scores, rating scales, and demographic and discharge data from the chart. Of 424 patients approached, 321 (76%) agreed to participate and 278 (65.6%) completed the test battery. Depression, anxiety, and organicity, measured by psychological tests, were significantly correlated with longer hospital stay. These correlations remained significant after the authors controlled for degree of physical impairment, emergency versus elective admission, and medical versus surgical service, which were themselves correlated with longer hospital stay. This study confirms a significant correlation between psychological comorbidity and length of stay after correcting for the methodological pitfalls found in earlier studies. The clinical, research, economic, and policy implications of these findings are discussed.