MacAndrew (1965) constructed the MacAndrew Alcoholism Scale (MAC) using adult male alcoholic outpatients and male psychiatric outpatients. Later, he developed the Substance Abuse Proclivity Scale (SAP; MacAndrew, 1986), specifically for screening younger males, using adolescent and young adult substance misusing and nonmisusing males 16 to 22 years of age. Because clinicians frequently apply the MAC to adolescents, we compared the efficacy of the MAC and the SAP scales using a sample of 436 young males between the ages of 13 and 25, who were hospitalized because of substance abuse, and 770 normal young males between the ages of 13 and 25. Results suggest that clinicians should use these scales with great caution.