Background: The determination of a treatment plan is one of the important stages for achieving a removable orthodontic treatment goals. The treatment plan is made by analyzing some obtained data. However, not all collected data is used because of some factors influence. One of collected data used in this research is the data from study model which applies Bolton and Howes index. Research Objectives: This research aimed to determine the conformity of removable orthodontic treatment plan from co-assistent in RSGM UMY with applying the calculation of Bolton and Howes index. Research Method: This research is an observational analytic research with cross sectional design. The sample of this study was a study model of co-assistent treated patients with removable orthodontic treatment plans in April 2016 - April 2017 at RSGM UMY. The treatment plan will be determined by measuring the study model using a sliding caliper then incorporated in Bolton and Howes index formula. Results: Based on chi-square test, there was a significant correlation between conformity and treatment plan, because p value (0.000) < 0,05. The percentage of conformity between co-assistant RSGM UMY treatment plan and Bolton and Howes index was 27.9%, which only 51.5% for Bolton index and 60.3% of Howes index. Conclusion: The research found that there is a relationship between conformity and removable orthodontic treatment plan based on the Bolton and Howes index and treatment plan in RSGM UMY.