Objective: to assess the validity of Little Irregularity Index in both the maxillary and mandibular arches. Materials and methods: The study was an invitro retrospective trial performed in the Digital Center of the Orthodontic Department, Faculty of Dentistry, Ain-Shams University. The study was conducted on 100 maxillary and 100 mandibular study casts representing a wide range of crowding. Prior to the initiation of the study, all study casts were converted into digital models by the primary investigator. The study procedure was divided into two phases. Phase 1, where five orthodontic professors assessed the 200 study casts selected for the study to assign a subjective score describing the anterior crowding and phase 2, where Four examiners of different orthodontic background levels used the digitized version of the study models to determine quantitatively the amount of anterior crowding as recommended by Dr. Little. Results: ICC for the maxillary and mandibular scores by the five orthodontic professors was notably high (>0.97). Also, for the measurements conducted by the four examiners on the digital models of both arches were (>0.99). The LOA were excessively broad in the maxillary scores, (2.42 + 9.84) = 12.26. Likewise, for the mandibular scores the LOA were again too extensive, (2.67 + 8.17) = 10.84. CCC values between the scores of the five orthodontic professors and the scores of the four examiners for the maxillary was 0.418 and for the mandibular was 0.534. Conclusion: The validity of LII in the maxillary and mandibular arches could not be confirmed.