The objective of the study was to describe the ovarian abnormalities of horse mackerel, Trachurus trachurus (Linnaeus, 1758), and to investigate the relationships that may exist between these abnormalities and nematode parasite infestation. 953 specimens of T. trachurus were randomly sampled between February 2013 and March 2014. A biometric analysis was conducted for every fish specimen. After dissection, parasites were collected, identified and the infestation rate was calculated. A macroscopic and microscopic study of the gonads was carried out for the infested and non infested fish specimens. The results revealed that only one ovary of the total sample examined had a morphological malformation. However, the microscopic study revealed that almost all the infested females had abnormalities: cyst and atresia increased for 17% and 38% of the examined sub-sample, respectively. The current results showed clearly that ovarian abnormalities were observed in large and old females, which were the most infested.