Environmental pollution, sedentary lifestyles, and unhealthy dietary patterns have been hypothesized as the main modifiable factors of human semen quality decline. The study aimed to assess the associations between an a priori-defined Mediterranean diet (MedDiet) adherence and semen quality parameters or medically assisted reproductive (MAR) outcomes in males. A systematic review was conducted with studies from PubMed, Embase, or Scopus databases until October 2024. A priori-defined MedDiet adherence was considered as exposure and conventional semen quality parameters as the primary outcomes. Secondary outcomes included MAR outcomes, reproductive hormone concentrations, and sperm DNA fragmentation. A quality assessment was performed using the NHLBI tool. Meta-analysis was conducted following Cochrane guidelines. A subgroup analysis was done for healthy participants and those from fertility clinics separately. A sensitivity analysis was performed to check the influential studies. A qualitative analysis was performed on 11 eligible articles (n = 2558 individuals). Data from 9 observational studies showed a positive association between the adherence to MedDiet and semen volume (1/9), sperm concentration (5/9 studies), count (5/9), total motility (5/9), progressive motility (4/9), vitality (1/9), normal morphology (2/9), or follicular stimulating hormone (1/9). Among these, the links between MedDiet adherence and MAR outcomes were prospectively explored only in 1 study, which reported no association. A total of 8 studies were eligible for meta-analysis (n = 1835 individuals). Total MedDiet adherence showed a significant positive association with sperm count (24.37 M spz.; 1.30-47.44; I = 89%), total motility (8.81%; 2.26-15.37; I = 88%), progressive motility (7.49%; 1.47-13.50; I = 86%), and normal morphology (1.02%; 0.21-1.82; I = 77%). Evidence from 2 randomized clinical trial evaluating the effect of MedDiet on semen parameters aligns with the primary results. Evidence from observational studies and clinical trials shows potential benefit of adhering to a MedDiet in terms of seminal quality parameters, but not fertility outcomes. This study was registered at PROSPERO as CRD42024584003.