A randomised controlled trial evaluated the effectiveness of the Integrated Employment Success Tool (IEST (TM)) in improving employers self-efficacy in modifying the workplace for individuals on the autism spectrum. Employers (N = 84) were randomised to the IEST (TM) or support as usual groups. Measurements of self-efficacy, knowledge and attitudes towards disability in the workplace were obtained at baseline and post-test. Results revealed a significant improvement in self-efficacy within the IEST (TM) group between baseline and post-test (p = 0.016). At post-test, there were no significant differences between groups in relation to self-efficacy in implementing autism-specific workplace modifications and employer attitudes towards disability in the workplace. Given the lack of significant outcomes, further research is needed to determine the effectiveness of the IEST (TM) for employers.Trial registration: Australian New Zealand Clinical Trials Registry #ACTRN12614000771651, registered 21/7/2014. Trial URL https ://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=366699.