Background: This study aimed to determine the gender of a sample of Iraqi adults using the mesio-distal width of mandibular canines, inter-canine width and standard mandibular canine index, and to determine the percentage of dimorphism as an aid in forensic dentistry. Materials and methods: The sample included 200 sets of study models belong to 200 subjects (100 males and 100 females) with an age ranged between 17-23 years. The mesio-distal crown dimension was measured manually, from the contact points for the mandibular canines (both sides), in addition to the inter-canine width using digital vernier. Descriptive statistics were obtained for the measurements for both genders; paired sample t-test was used to evaluate the side difference of mandibular canines in both genders, independent samples t-test was performed to evaluate the gender difference in addition to the percentage of dimorphism and percentages of correctly classified and misclassified cases using the standard mandibular canine index. Results: The mesio-distal widths of the mandibular canines were non-significantly slightly larger in males than females, while the inter-canine width was larger in males than females with a high significant difference. The accuracy of genders determination using standard mandibular canine index was 32% for males, 59% for females and 45.5% for the combined sample. The percentages of dimorphism were 0.58% for the canine mesio-distal width, 3.99% for the inter-canine width and 3.85 for the mandibular canine index. Conclusions: The mandibular inter-canine width and mandibular canine index gave better percentage of dimorphism than the mesio-distal width of mandibular canines. On the other hand, standard mandibular canine index showed low accuracy for gender determination.