Background: Unhealthy eating habits and physical inactivity constitute an emerging public health problem. The working population is of special interest for public health monitoring and evaluation because workers’ unhealthy lifestyles may lead to reduced work ability. The aim of this study was to determine diet quality and adherence to the Mediterranean diet (MD), according to the level of physical activity, and to detect variables associated with the working population’s being highly physically active. Material and Methods: At the Institute for Occupational Medicine 400 full-time workers were examined for obesity factors, filled in the short version of International Physical Activity Questionnaire (IPAQ-short) and a validated food frequency questionnaire for adherence to the Mediterranean diet using Mediterranean Diet Score (MDS). The workers were divided into low, moderate and high physical activity groups according to the IPAQ-short scoring protocol. Hierarchical linear regression was performed to determine the variables associated with being highly active. Results: One-third of the participants were highly physically active and their diet adhered to the MD (Me_MDS = 7). Significant variables associated with a high level of physical activity were gender (p < 0.001), age (p = 0.02), waist-to-hip ratio (WHR) (p < 0.001), sitting level (p = 0.044) and occupational type (p < 0.001). Conclusions: It was found that the participants displaying a high level of physical activity had a better quality diet that adhered to the Mediterranean diet but not to a significant degree. The variables associated with a high level of physical activity were male gender, younger age, normal WHR, non-sedentary occupation and reduced sitting time. The study findings could serve the purpose of improving future public health promotion of physical activity and the Mediterranean diet. Med Pr. 2019;70(2):169–76