Objective: Adolescent patients' conduct disorder and substance use disorder symptoms are "risky behaviors" with unpredictable rewards and punishments. The authors asked whether such youths also take excessive risks in new situations without prior learning, peer pressure, or intoxication. Method: Subjects were 20 adolescent patients in a program treating conduct disorder and substance use disorder and 20 controls. All were substance free [greater than or equal to] 7 days; underwent substance-related, psychological, and social assessments; and performed the Balloon Analogue Risk Task: mouse presses inflated a computerized "balloon" image, each press earning 1 cent. The 30 balloons "popped" at unpredictable sizes; earnings from popped balloons were lost. A "Collect" response saved current earnings and advanced to the next balloon. Results: Mean number of inflating presses: patients, 1021 and controls, 705 (p = 0.001); group differences were stable from the task's beginning. Mean inflating presses before a "collect" response: patients, 38.6 and controls, 24.0 (p = 0.0005). Mean balloons popped: patients, 9.8 and controls, 6.3 (p = 0.001). Patients (versus controls) reported more aggressiveness and substance use and perceived less risk from substances. Patients' responses were significantly slower than those of controls. Conclusions: From the beginning of this novel task, conduct disorder and substance use disorder patients (compared with controls) took more risks, indicating an initial risk-taking propensity, although patients' slower responses argued against "impulsive, thoughtless" behavior. (Contains 3 figures and 1 table.)