This report presents the results of a test-retest reliability study of the alcohol and drug dependence, as well as harmful use/abuse were investigated in Ankara, Turkey and Farmington, Connecticut (US). Reliabilities for the past year, prior to past year, and lifetime diagnosis of alcohol and drug use disorders were evaluated using ICD-IO, DSM-III-R and DSM-IV criteria. The results indicate that SCAN alcohol and drug diagnosis have good to excellent levels of reliability for dependence across different substances, different diagnostic systems, and different cultural groups. Diagnostic classification of alcohol and drug abuse/harmful use was considerably less reliable. Implications of the findings are discussed.