Various case finding techniques have been employed in the study of narcotic addiction. Each method contains its own bias, though their nature and extent are often not clear. This study was undertaken to evaluate the bias of three case finding techniques: (1) a field survey of addicts (n = 28), (2) patients voluntarily seeking treatment for addiction at the medical facility (n = 81), and (3) patients voluntarily seeking help for addiction at a Buddhist monastery (n = 118). All subjects belonged to the Hmong ethnic group, a tribal people of southeast Asia who grow the opium poppy as a cash crop. Despite the variability in sampling methods, most factors did not show significant differences. These included sex ratio, marital status, occupation, duration of addiction, and number of opiate doses per day. Some differences were noted in current age, age at addiction, and mode of using opium. Possible causes for those observed differences are explored.