The clinical assessment of drug-taking behaviors in medically ill patients with pain is complex and may be hindered by the lack of empirically derived information about such behaviors in particularly medically ill populations. To investigate issues surrounding the assessment of these behaviors, we piloted a questionnaire based on the observations of specialists in pain management and substance abuse. This preliminary questionnaire evaluated medication use, present and past drug abuse, patients' beliefs about the risk of addiction in the context of pain treatment, and aberrant drug-taking attitudes and behaviors. This instrument was piloted in a mixed group of cancer patients (N = 52) and a group of women with HIV/AIDS (N = 111). Reports of past drug use and abuse were more frequent than present reports in both groups. Current aberrant drug-related behaviors were seldom reported, but attitude items revealed that patients would consider engaging in aberrant behaviors, or would possibly excuse them in others, if pain or symptom management were inadequate. Aberrant behaviors and attitudes were endorsed more frequently by the women with HIV/AIDS than by the cancer patients. Patients greatly overestimated the risk of addiction in pain treatment. We discuss the significance of these findings and the need for cautious interpretation given the limitations of the methodology. This early experience suggests that both cancer and HIV/AIDS patients appear to respond in a forthcoming fashion to drug-taking behavior questions and describe attitudes and behaviors that may be highly relevant to the diagnosis and understanding management of substance use among patients with medical illness.