Background: There is a pronounced controversy regarding the dental and mental consequences of thumb sucking habit, which is a familiar nonnutritive pattern of sucking. Commonly, this behavior is harmless, yet those who sustain this pattern may have dental alterations and emotional difficulties. Children’s intelligence level influences their capabilities to judge, evaluate and handle priorities and/or problems profoundly and precisely. Thumb sucking habit might be a manner of liberating the psychological tenseness among several children. Objective: The purpose of this study is to assess the prevalence of thumb sucking habit and its relation to the eruption of permanent teeth and IQ among children aged 6-7 years old. Subjects and methods: In Karbala city, Iraq, a cross-sectional study was performed through which an over-all of (1222) students at primary schools, 6-7 years old, were included. Questionnaires answered by the parents were used for collecting information regarding the presence of thumb sucking habit. All the students were examined clinically for the stage of eruption of their permanent teeth. Concerning the intelligence quotient (IQ) it was estimated by means of the colored progressive matrices of Raven’s test. Data was statistically analyzed utilizing SPSS version 21. Results: The present study revealed that the prevalence of the thumb sucking habit amongst the whole sample was (7.61%), it was more predominant in the below average IQ category of children (8.99%). Furthermore, it was found that children who practiced the habit had a delay in the eruption of their permanent teeth. Yet, these results showed no statistical significance. Conclusion: There is an association between thumb sucking habit in children, their intelligence level and the eruption of their permanent teeth, by which the habit was practiced more by children of below average category of intelligence and the eruption of permanent teeth among those who performed the habit was delayed however this result was not significant statistically. Key words: Intelligence quotient (IQ), Permanent teeth, Karbala, Thumb sucking