Sensory Integration Therapy (SIT) is a popular treatment for Pervasive Developmental Disorders that involves therapists using various strategies and manipulanda to provide sensory stimulation to improve behavioral dysfunctions. Although SIT is popular, the research literature demonstrates little experimental proof of effectiveness. Many published studies find little to no causal relationship between SIT and improvements in target behaviors. There are numerous internal and external validity threats that preclude confidence in a functional relationship for those studies that report positive changes. The current study attempted to evaluate the impact of different SIT techniques on the behavioral excesses of children diagnosed with autism, while using research designs that adhered to commonly accepted standards for internal and external validity controls. The results showed that there was no causal relationship between the sensory procedures and improvements in the targeted dependent variables. Thus, SIT remains an unproven treatment for autism.