This study aims to investigate the association between prenatal exposure to terbutaline and other beta2 adrenergic receptor (B2AR) agonists and autism spectrum disorders (ASDs). The methodology used is a case-control study among children born from 1995 to 1999 at Kaiser Permanente Northern California hospitals. Cases (n = 291) were children with an ASD diagnosis; controls (n = 284) were children without ASDs, randomly sampled and frequency-matched to cases on sex, birth year, and delivery hospital. Exposure to B2AR agonists during 30 days prior to conception and each trimester of pregnancy was ascertained from prenatal medical records and health plan databases. The frequency of exposure to any B2AR agonist during pregnancy was similar for mothers of children with ASD and mothers of controls (18.9% vs. 14.8%, P = 0.19). Exposure to B2AR agonists other than terbutaline was not associated with an increased risk for ASDs. However, terbutaline exposure for >2 days during the third trimester was associated with more than a fourfold increased risk for ASDs independent of indication although the limited sample size resulted in an imprecise and nonsignificant effect estimate (OR(adj) = 4.4; 95% confidence interval, 0.8-24.6). This analysis does not offer evidence linking B2AR exposure in pregnancy with autism risk. However, exposure to terbutaline during the third trimester for >2 days may be associated with an increased risk of autism. Should this result be confirmed in larger samples, it would point to late pregnancy as an etiologic window of interest in autism risk factor research.