Additional treatment after inpatient detoxification is recommended; however, many patients fail to initiate aftercare. The purpose of this observational study was to determine which patients hospitalized for alcohol or drug withdrawal subsequently fail to initiate recommended outpatient aftercare treatment by using existing data from medical records. Of 406 patients, 180 (44.3%) did not initiate outpatient aftercare treatment after hospitalization for detoxification. Compared with those who did initiate aftercare, those who did not were less likely to have education beyond high school (44% vs. 32%; P = 0.018), to be enrolled in a managed care health insurance plan (46% vs. 34%; P = 0.013), and to have a family history of chemical dependency (81% vs. 72%; P = 0.049). These values were similar with multiple regression analysis. Of the 406 patients, 11 of 56 (20%) without any of these risk factors, 145 of 314 (46%) with 1 or 2 risk factors, and 24 of 36 (67%) with all 3 of these risk factors did not keep scheduled outpatient appointment for aftercare. These findings suggest that some patients admitted for inpatient detoxification, identifiable by certain admission characteristics, are at risk for failure to link with appropriate outpatient aftercare treatment.