To determine the malocclusion complexity and orthodontic treatment need in urban Iranian schoolchildren using the Index of Complexity, Outcome, and Need (ICON) and the Index of Orthodontic Treatment Need (IOTN) and to also assess the relationship between these indices.The study sample comprised 502 individuals (253 girls and 249 boys, 11 to 14 years of age), of whom one girl and five boys already had an orthodontic appliance at the time of the survey. In those individuals not wearing orthodontic appliances (n=496), the definitive treatment need (ICON>43) and compartments of the ICON were defined and compared between sexes. The Aesthetic Component and Dental Health Component (DHC) of the IOTN were also recorded. Scatter plots and Spearman rank correlation coefficients were used to explore the relationships between the ICON and DHC and the Aesthetic Component (AC) of the IOTN.According to ICON, DHC (IOTN), and Aesthetic Component (IOTN), 46.6%, 36.1%, and 17.9%, respectively, of the studied children needed orthodontic treatment; however, only 1.1% wore an appliance. In terms of complexity, 26.4% of the studied individuals were considered to have a difficult or very difficult malocclusion. With regard to treatment needs, significant correlations existed between the ICON scores and DHC (IOTN) (r=0.93) and between the ICON scores and the esthetic component (IOTN) (r=0.96). The threshold for treatment need was lower in the ICON than in the IOTN. Of the children who were classified in the borderline category of the IOTN (DHC=3), 52.0% were in need of treatment according to their ICON score (ICON>43). No sex difference was found for treatment need (ICON>43, P>.05) and treatment complexity (P>.05).According to the ICON, 46.6% of the Iranian schoolchildren need orthodontic treatment. ICON is a good substitute for the IOTN, yet it results in a lower treatment-need threshold.