The "autism spectrum disorder observation for children" ("ASD-OC") is a newly created 54-item observation measure for autism spectrum disorders (ASD). Due to the fact that many of the ASD observation measures currently available do not have established psychometric properties and require extensive time and training to administer, the "ASD-OC" seeks to address these issues. The purpose of this initial study was to investigate the reliability of the "ASD-OC". The measure was administered to a sample of 114 children as part of an outpatient evaluation. In a subset of the sample, 26 children were rated by two independent clinicians after the same session. Interrater reliability was calculated using intraclass coefficients (ICC). Five items were removed after this interrater reliability analysis given poor reliability coefficients less than 0.40. Mean interrater reliability for each of the 49 retained items was good (i.e., 0.73). Interrater reliability for the scale as a whole was excellent (i.e., ICC = 0.96). Item analysis and internal consistency were investigated in the total sample (n = 114). Four items were removed from the scale because of little to no variance in scores. Forty-five items remained on the scale. The internal consistency of the "ASD-OC" as measured by Cronbach's alpha was excellent at 0.96. The "ASD-OC" proved to be a promising measure with robust reliability. (Contains 2 tables.)