The Halikas-Crosby Drug Impairment Rating Scale for Cocaine (HAL DIRS-C) is designed to measure improvement in drug treatment through interval assessment of impact of cocaine use on daily functioning, relationships with other people, other alcohol and drug use, cocaine withdrawal symptoms, adverse effects associated with cocaine use, and personal outlook over the previous week. The scale is a 25-item clinical rating scale administered in the context of a semistructured interview (modeled after and similar to the Hamilton Rating Scale for Depression). The HAL DIRS-C was administered weekly to 147 subjects participating in a 12-week, double-blind medication trial with a psychosocial treatment component. Without breaking the pharmacologic blind, the HAL DIRS-C score was found to be significantly related to study retention, ongoing psychosocial treatment participation, urinalysis results, and other measures of outcome. The results support the validity of the HAL DIRS-C as a standardized measure of improvement or outcome in clinical research involving the treatment of cocaine abuse.