A changing criterion design was used to examine the effects of two stimuli (a green card and a red card), conditioned via discrimination training, on reducing motor and vocal stereotypy in a youngster with autism while he looked at books. During discrimination training, motor and vocal stereotypy was not interrupted in the presence of a green stimulus, but was interrupted in the presence of a red stimulus using manual guidance and appropriate behavior was reinforced. After the participant demonstrated successful discrimination of the stimuli (i.e., the absence of stereotypy in the presence of a red stimulus and the engagement in stereotypy in the presence of a green stimulus), intervention began. During intervention, upon meeting criterion for latency to engage in motor and vocal stereotypy in the presence of the red stimulus for a target duration, the participant was provided access to the green stimulus, which signaled that motor and vocal stereotypy would not be interrupted. The criterion latency to engage in stereotypy in the presence of the red stimulus was systematically increased. Simultaneously, the duration of access to the green stimulus was systematically decreased. The red and green stimuli were faded from poster boards to colored 10 × 10 cm cards, and stimulus control was generalized to the participant's classroom and to a community setting (i.e., public library). Results are discussed in terms of discrimination training as a useful intervention for reducing motor and vocal stereotypy. Copyright © 2011 John Wiley & Sons, Ltd.