The aim of this retrospective study was to evaluate the effects of a group of factors on the duration of orthodontic therapy of Angle Class I malocclusion patients. Material and Methods This retrospective study included 276 (66 males and 210 females) finished Angle class I patients. The sample was gathered from 2 private clinics (132 patients) and one dental school, orthodontic department of Cairo University, (144 patients). Factors that were investigated included ,gender, age, oral hygiene, missed appointments, elastic wear, broken appliances, amount of overbite / open bite, maxillary mandibular plane angle (MMP), ANB, transverse discrepancies, impacted teeth, amount of crowding, extraction versus nonextraction, type of clinic (private clinic vs. dental school), and treatment duration. Results and Conclusions 1. The numerical values (age, overbite, openbite, MMP, &ANB) all had no statistically significant correlation with the treatment duration, EXCEPT the ANB. There was a statistically significant positive (direct) correlation between treatment duration and ANB. 2. Males showed a statistically significant longer mean treatment duration than females. 3. When oral hygiene, elastic wear, and broken appliances were correlated with treatment duration, the results were not statistically significant. 4. When correlating missed appointments with treatment duration, Patients with (Poor) grades showed the statistically significant highest mean treatment duration, this was followed by (Fair) then (Good) grades. Patients with (Excellent) grades showed the statistically significant lowest mean treatment duration. 5. There was no statistically significant difference between mean treatment durations in public and private clinics. 6. Patients with severe crowding showed the highest statistically significant mean treatment duration. This was followed by moderate crowding, then patients with spacing. Patients with mild crowding showed the lowest statistically significant mean treatment duration. 7. There was no statistically significant difference between mean treatment durations among patients with different transverse discrepancy findings. 8. Patients with more than one impacted tooth showed the highest statistically significant mean treatment duration. This was followed by patients with one impacted tooth. Patients with no impactions showed the lowest statistically significant mean treatment duration. 9. Treatment plans involving extractions showed a higher statistically significant mean treatment duration than non-extraction treatment plans.