1-hydroxypyrene (1-OHP) is a biomarker of exposure to polycyclic aromatic hydrocarbons (PAHs). PAHs are pollutants produced by the combustion of organic material, and could be found both indoors and outdoors. Prenatal exposure to these compounds has been associated with retarded intrauterine growth and respiratory problems in children. The objective of this study is to describe the 1-OHP levels in urine in pregnant women in the INMA cohort in Valencia, and to study the association with socio-demographic and lifestyle variables, as well as with indicators of air pollution. The study population is a sub-sample (n: 204) of a cohort of pregnant women in the multicentre INMA project in Valencia (Spain). Urine samples were taken in week 12 of gestation, and 1-OHP was analyzed, and adjusted for creatinine. Socio-demographic and lifestyle information was collected using a questionnaire. Data from the monitoring stations in Valencia were used to assign levels of exposure to nitrogen dioxide (NO2), sulphur dioxide (SO2), total suspended particulates (TSP) and carbon monoxide (CO). The median 1-OHP level was 0.061 muicrool/mol of creatinine. Women who smoked had higher 1-OHP levels (0.095 micromol/mol of creatinine) than non-smokers (0.050 micromol/mol of creatinine). The variables predicting 1-OHP levels on linear multivariate analysis were: tobacco consumption, consumption of fried and smoked foods. There was also a significant association with NO2 levels 4 and 5 days before the samples were taken. The 1-OHP levels found in pregnant women in Valencia were higher than those found among women in reports in USA. 1-hydroxypyrene could be a good marker of exposure to PAHs from tobacco and diet, and also a useful marker of short term exposure to air pollution.