The human orbit is a complex bone structure, which lodges the visual apparatus. Its dimensions are among the craniofacial variables that are successfully used in anthropology, oral and maxillofacial surgery or in forensic research. Also, the morphometric variability of orbit and its role in the sexual dimorphism are topics achieved in paleoanthropological studies. In the present study, we propose to debate the sexual dimorphism by the Orbital Index. The orbital index represents the relation between the height and the breadth of orbit. The linear measurements (i.e., orbit height and breadth) come from a sample consisting of 134 human skulls of 16th – 19th centuries. Skeletons were excavated from three necropolis of the Iasi city, Romania: „Sfântul Nicolae – Ciurchi” Church, the „Banu” Church and the necropolis located in the eastern part of the ancient “Curtea Domneasca”. The sexual dimorphism was analysed by using discriminant function analysis. Results are in 95% confidence range and p < 0.05 was considered significant. All statistical analyses were performed by XLStat 2020.4.1. The study results reveal that the anthropometric differences of the orbit derive from sex, and the age has no influence (p 0.003). The average orbital index in females is 84.33, and in males is 81.16. Discriminant analysis technique (DA) has demonstrated a high efficiency in the sex determination using the orbits of the human skull. This was observed when the orbital index was correlated with other facial indices. Discriminant function equations have been derived from various combinations of these variables emphasizing the dimorphic role of the orbit in medieval human population of Iasi city. Correct classification rates produced by Cross-validation varied from 50% to 84%. This study show that the Orbital Index could be used in the sex determination, especially for incomplete skeletons, when other differentiation criteria cannot be applied.