AimTo assess the prevalence of occlusal anomalies and deleterious oral habits and to determine the association between these habits and the presence of occlusal anomalies. Methods1176 children between the ages of 3 and 13 years old were observed in “Paranhos Sorridente” project at the Faculty of Dentistry of University of Porto's clinic. Statistical analysis was performed using the statistical analysis program SPSS® v.19.0. The level of significance was set at 0.05. ResultsOcclusal anomalies were detected in 29.2% of the children: 11.2% had anterior open bite; 4.8% had posterior open bite; 9.2% had anterior cross-bite; and 16.1% had posterior cross-bite. Deleterious oral habits were detected in 33.8% of the children: 2.4% had pacifier sucking habits; 3.8% lip sucking; 1.9% tongue sucking; 4.5% thumb sucking; 2.3% other finger sucking; 7.6% lip biting; 29.3% nail biting; 5.1% tongue thrusting; and 1.4% cheek biting. Of the 381 children with deleterious oral habits, 130 (34.1%) had occlusal anomalies (p=0.009). ConclusionDeleterious oral habits have a significant prevalence and are often associated with occlusal anomalies.