This study assessed factors associated with extended length of stay (ELOS) for patients presenting to a psychiatric emergency service (PES). Two hundred six subjects with a length of stay of 24 h or longer were compared with time-matched controls (patients that presented directly after the ELOS patient). Binary logistic regression was used to identify risk factors for ELOS. ELOS was associated with suicidal ideation, disposition to an inpatient unit, homicidal ideation, lack of insurance, homelessness, male gender, past history of psychiatric hospitalization, diagnosis of substance abuse, significant psychiatric co-morbidity (represented by three or more Axis I diagnoses), and diagnosis of a psychotic disorder. Lack of insurance, suicidal ideation, disposition to inpatient unit, and homicidal ideation all made nonredundant contributions to predicting stays of 24 h or longer.