Few studies have examined associations between polycyclic aromatic hydrocarbons (PAHs) and birth outcomes, and no studies have been conducted in El Paso County Texas, along the United States-Mexico border. Infants born from 2005–2007 to Hispanic mothers with a birth weight less than the 10th percentile for gestational age and sex were classified as small for gestational age (SGA). PAH exposures were estimated for the entire period of gestation and for each trimester of pregnancy using ambient air monitoring data from 2004–2007. Logistic regression was used to estimate odds ratios for the association between PAH levels and SGA infants. There was marked seasonal variation in the carcinogenic PAHs. Established risk factors for SGA were observed to be associated with SGA births in this population. No associations were detected between PAH levels and SGA births. These findings provide no evidence of an association between PAHs and SGA infants.