This research focused on investigating the basal serum concentrations of polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in the general population residing in two urban-industrial zones near and far from an energy recovery plant under construction in Gipuzkoa, Basque Country (Spain). The study used a cross-sectional design and included 227 participants who were randomly selected from municipal censuses in both areas. The participants were stratified based on age (ranging from 18 to 70 years) and sex. Serum samples were collected from the participants and analysed following the established protocol to measure the concentrations of PCDD/Fs and dl-PCBs. The study used multiple linear regression models to assess the impact of various sociodemographic variables, lifestyle factors, reproductive history, and diet on the variability of the measured compounds in the participants' serum. The median total toxicity equivalent (TEQ) in serum, was 10.58 pg WHO-TEQ2005 g-1 lipid. Serum PCDD levels were lower in the population residing in the "far" zone than the "near" zone. Age was positively associated with both PCDD/F and dl-PCB levels, indicating that older participants had higher concentrations of these compounds in their serum. This finding might be attributed to cumulative exposure over time. In terms of sex differences, women exhibited lower levels of dl-PCBs compared to men. Among lifestyle factors, smokers showed lower levels of dl-PCBs compared to non-smokers. Furthermore, daily alcohol consumption was significantly associated with higher serum levels of these compounds, with daily drinkers showing higher levels than non-drinkers. Consumption of local poultry was associated with significantly higher serum levels and oil consumption with low levels of PCDD/Fs.