A cross-sectional sero-epidemiological study was conducted on teen-agers in Northern Sardinia, a low risk population for Lyme borreliosis. The adjusted sero-prevalence estimate for Enzyme Linked Immunofluorescent Assay on 443 teen-agers (229 males and 214 females) was 6.1%. The females vs males Odds Ratio was 5.1 (CI95%: 2.1-12.8). The prevalence was associated with the family size (chi2 for trend: p=0.03); teenagers without cohabitants, except parents, had a five fold risk (CI95%: 1.2-20.7) of sero-positivity in comparison to those with wider families. No significant association was found with other socio-economical indices nor with pet-owning. In conclusion, positive Lyme serology is not common in Northern Sardinia, but further sero-epidemiological survey on at high-risk population (forestry workers, hunters, shepherds) are needed.