This study examined the measurement tools and target symptoms/skills used to assess treatment response during Autism Spectrum Disorder (ASD) intervention trials from 2001 through 2010. Data from 195 prospective trials were analyzed. There were 289 unique measurement tools, of which 61.6% were used only once, and 20.8 % were investigator-designed. Only three tools were used in more than 2% of the studies, and none were used in more than 7% of studies. Studies investigated an average of 11.4 tool-symptom combinations per trial, with as many as 45 in one study. These results represent a lack of consistency in outcome measurements in ASD intervention trials. These findings highlight the need to set guidelines for appropriate outcome measurement in the ASD field.