This study aims to clarify relationships of maternal psychiatric conditions and selective serotonin reuptake inhibitor (SSRI) use during preconception and pregnancy with risk of neurodevelopmental disorders in offspring. We used data from the Study to Explore Early Development, a multisite case-control study conducted in the United States among children born between 2003 and 2011. Final study group classifications of autism spectrum disorder (ASD) (n = 1367), developmental delays or disorders (DDs) (n = 1750), and general population controls (n = 1671) were determined by an in-person standardized developmental assessment. Maternal psychiatric conditions and SSRI use during pregnancy were ascertained from both self-report and medical records. We used logistic regression to evaluate associations of ASD and DDs (vs. population controls) with maternal psychiatric conditions and SSRI treatment in pregnancy. To reduce confounding by indication, we also examined SSRI associations in analyses restricted to mothers with psychiatric conditions during pregnancy. Psychiatric conditions and SSRI use during pregnancy were significantly more common among mothers of children with either ASD or DDs than among population controls. Odds of ASD were similarly elevated among mothers with psychiatric conditions who did not use SSRIs during pregnancy (adjusted odds ratio 1.81, 95% confidence interval 1.44-2.27) as in mothers who did use SSRIs (adjusted odds ratio 2.05, 95% confidence interval 1.50-2.80). Among mothers with psychiatric conditions, SSRI use was not significantly associated with ASD in offspring (adjusted odds ratio 1.14, 95% confidence interval 0.80-1.62). Primary findings for DDs exhibited similar relationships to those observed with ASD. Maternal psychiatric conditions but not use of SSRIs during pregnancy were associated with increased risk of neurodevelopmental disorders in offspring.