Can preconception adherence to a Mediterranean diet influence the rate of poor response to ovarian stimulation in IVF cycles? The impact of dietary habits on the success of IVF is controversial. Inconsistencies may be explained by confounders associated with the use of pregnancy as an outcome as well as by a reductionist view of diet that focuses on single components rather than on food patterns. This cross-sectional study analysed adherence to a Mediterranean diet in women with unexpected poor response to ovarian stimulation. Main inclusion criteria were: age 18-39 years, normal weight, preserved ovarian reserve and starting dose of gonadotrophins of 150-225 IU/day. Adherence to the Mediterranean diet was assessed through a Mediterranean diet score (MDS). Unexpected poor ovarian response was defined as the retrieval of ≤3 suitable oocytes. A total of 296 women were included, of whom 47 (15.9%) showed an unexpected poor response. A clear dose-related association with tertiles of MDS was not observed in the univariate analysis. However, in the multivariate analysis, the risk of unexpected poor response was significantly lower for women in the second tertile of MDS compared with the first tertile (adjusted odds ratio [OR] 0.29, 95% confidence interval [CI] 0.11-0.76) and for women in the second and third tertiles, grouped together, compared with the first tertile (adjusted OR 0.34, 95% CI 0.14-0.82). Low adherence to a Mediterranean diet could be a risk factor for unexpected poor ovarian response.