The ability of respondents to underreport successfully on substance abuse and validity scales of the Minnesota Multiphasic Personality Inventory-Adolescent (MMPI-A; Butcher et al., 1992) was evaluated. Incarcerated teens (67 substance abusing, 59 non-substance abusing) completed the MMPI-A twice: once under standard instructions (SI) and once under instructions to fake good (FG). Under SI, substance scales correctly classified about 60% to 85% of adolescents. Under FG, substance- and non-substance-abusing juveniles produced lower scores on substance scales. However, the Lie Scale (L) was able to detect more than 75% of deceptive profiles and about 77% of honest profiles. When scale L and the best substance scale were used in combination, only about 18% of faking substance abusers were not identified as either substance abusers or as underreporting. For feigning substance abusers, only about 10% of substance abusers were detected, with about 72% being categorized as faking and needing further assessment.