Little is known about the effect of non-nutritive sucking habits (pacifier and digital sucking) in the prevalence of molar Class in mixed dentition. The aim of this study was determinate the relation between non-nutritive sucking habits, and Angle´s molar Class, in the horizontal plane, and it´s relation with gender. A convenience sample of 326 children with ages between 6 and 12 years was selected from three schools of Oporto. To collect the epidemiologic data, was used a method recommended by the WHO. An indirect questionnaire about the medical history, dental habits, was used. It was adapted from Sanchez-Molins and validated by Clinical Dental III of Integrated Dental University Institute Health Sciences, Gandra, Portugal. In this study, 326 infants were examined in order to determine the prevalence of non-nutritive sucking habits. Only 45 observed children did not mentioned any kind of non-nutritive sucking habit; the remaining 281 children mentioned at least one potential bad habit. Children with non-nutritive sucking habits show a higher molar Class II percentage in females, while molar Class III is more frequent among males compared with children with no sucking habits. Children with non-nutritive sucking habits, presented a higher-Class II prevalence with statistically significance. It was detected a direct relationship between Angle´s molar Class and gender.