Background: The Mediterranean Diet (MD) has been associated with a reduced risk of developing several pathologies, such as cardiovascular diseases. Despite this, adherence to MD in the general population has decreased in the past years. Due to COVID-19 crisis, eating habits of the population are being affected, thus data assessing these habits just before lockdown are important to determine how they are modified. The Mediterranean Diet Quality Index (KIDMED) questionnaire was used to evaluate adherence to MD just before COVID-19 lockdown.Methods: The KIDMED survey was launched through the Google platform for surveys, from 2/20/20 until 3/13/20. Additionally, questions about gender, weight and height for body mass index (BMI) calculation, academic degree, and nationality were included. Multivariate linear regression was performed for data analysis.Results: A total of 861 completed surveys were collected. Some surveys were discarded because data was missing (18), the participants were not of Spanish nationality (18), or because they did not belong to the age groups included in the study (19). The remaining 804 surveys were divided into the following age groups: 15-24 (n=160), 25-34 (n=158), 35-54 (n=363) and 55-69 (n=123). In the 15–24-year-old group, 71.9% had a BMI between 18-24.9, but only 28.1% reached an index ≥8 in the KIDMED questionnaire. Adherence to MD improved as the age in the groups increased, but so did the BMI, especially in the oldest group. In all adult groups, approximately 50% had a university education. Overall, lower BMI was significantly related to females, younger age and a higher degree of studies. On the other hand, the higher adherence to MD was related to older age and a higher degree of education. Conclusions: The improved adherence to MD was not associated with a reduced BMI. Maybe other factors, like sedentary life or hormonal changes, known to impact people while aging, have influenced our results. Possibly, adherence to MD might have played a protective role, at least partially, against an even higher BMI. More research is needed to fully determine the impact of adherence to MD in the Spanish population, also after COVID-19 lockdown.Keywords: Mediterranean diet, KIDMED, Body mass index, Spain