BACKGROUND: It is well known that environmental conditions are related to the risk of developing cardiovascular diseases and events. However, the mechanisms behind these relations are not well understood. One mechanism could be elevation of blood pressure. In this study we assessed associations between blood pressure and environmental conditions among citizens in Oslo, Norway. MATERIALS AND METHODS: We used the Oslo Health Study (HUBRO), a population based study of 18,770 Oslo citizens, to assess associations between blood pressure and environmental conditions including season, smoking, outdoor temperature and air pollution. RESULTS: Blood pressure was higher in the winter season, but the association disappeared when we adjusted for temperature. A 10 degrees C reduction in outdoor temperature, the day blood pressure was measured was related to an increase in blood pressure for both men [SBP: 1.5 mmHg (95% CI, 0.6-2.3); DBP: 1.3 mmHg (95% CI, 0.1-1.8)] and women [SBP: 2.4 mmHg (95% CI, 1.6-3.2); DBP: 1.8 mmHg (95% CI, 1.3-2.3)]. No convincing relation was found between indicators of air pollution exposure and blood pressure. CONCLUSION: Several environmental conditions were related to blood pressure, and have similar associations with cardiovascular diseases or mortality. This could indicate that some of the effect these exposures have on the cardiovascular system is by increasing blood pressure.