['It has been shown that maternal mental health is associated with poorer skills development in the offspring. However, the evidence evaluating the association between social anxiety disorder (SAD) and cognitive or language development, is scarce.', 'To evaluate the association between maternal SAD and performance in cognitive and language tests in 30-month old children.', 'This was a cohort study involving young women evaluated since pregnancy.', 'We evaluated 520 mother-child dyads who received prenatal medical assistance through the National Public Health System in a southern Brazilian city, from October 2009 to March 2011.', 'We used the Mini Neuropsychiatric Interview Plus (MINI Plus) to assess SAD among young mothers. Cognitive and language performance in their offspring was analyzed using the Bayley Scales of Infant and Toddler Development - 3rd Edition.', 'We found an association between maternal SAD and performance in cognitive and language tests. Children of mothers with SAD had in average 4.5 less points in the Bayley scale, when compared to those with mothers without SAD: in the cognitive (β=-4.53 [95% CI -7.8; -1.1] p=0.008) and language subscales (β=-4.54 [95% CI -9.0; -0.5] p=0.047).'] Is cognitive and language performance in children associated with maternal social anxiety disorder : A study of young mothers in southern Brazil?