The aim of this study is to investigate the association between prematurity and diagnosis of neurodevelopmental disorders (ND) (attention deficit/hyperactivity disorder [ADHD] or autism spectrum disorder [ASD]) in Brazilian children and adolescents. Case–control study based on medical records data from a specialized outpatient clinic. Prematurity was defined as gestational age less than 37 weeks. Prematurity was independently associated with diagnosis of a ND (adjusted odds ratio [AOR] 3.46, 95% CI 1.15 – 7.92), as well as with ADHD and ASD diagnosis after a multiple logistic regression analysis. These findings from Brazilian patients are related to what is found in the literature worldwide. Efforts to modify risk factors, such as prematurity, may impact incidence reduction of both ADHD and ASD.