Toxoplasmosis is a disease caused by the intracellular protozoan parasite, Toxoplasma gondii which infects up to one-third of the world human population. Toxoplasmosis in neonates and immunocompromised patients can lead to severe disease and death. We investigated the prevalence and risk factors for T. gondii infection in Iceland, Sweden and Estonia, and tested the hypothesis that T. gondii infection causes systemic inflammation and protects against atopy. Blood samples were collected from 1277 randomly selected subjects. The presence of T. gondii IgG antibodies was determined by an ELISA method and levels of Hs-CRP by immunoturbidimetric assay. The prevalence of T. gondii antibodies was 54.9% in Tartu, 23% in Uppsala and 9.8% in Reykjavik (p<0.0001). The risk of positive T. gondii antibodies increased with the number of siblings and with age in Sweden. T. gondii infection was associated with asthma related symptoms and increased Hs-CRP (p = 0.02). No association was found with IgE-sensitization and lung function. We concluded that risk factors for T. gondii infection suggested that soil exposure was 1 of the mechanisms in all 3 countries and a meat-associated infection route is a risk in Sweden.