Objective: To compare the Index of Orthodontic Treatment Need (IOTN) in class I and class II malocclusions. Material and methods: The sample was 50 class I and 50 class II study models for a total of 100 models. The models were evaluated with the IOTN, tabulated and the descriptive statistics were calculated with the Microsoft Office Excel 2007 program. Results: The need for treatment was 26% in class I malocclusion and 58% in class II. When evaluating the sample with the dental health component the need for orthodontic treatment was found that 72% of the sample needed some type of orthodontic treatment in class I and 100% in class II. With the aesthetic dental component 74% were found to have little or no need for orthodontic treatment in class I and 42% in class II. Conclusions: The results of the IOTN in patients requesting treatment was higher in class II malocclusion than in class I malocclusion.  (Rev Esp Ortod. 2020;50(2):2-052-056)