
Background: Parents are frequently concerned about their children's behavior patterns especially if they are repetitive or stereotyped.The term thumb sucking refers to placing thumb into the mouth many times every day and night, exerting definite sucking pressure. Prevalence of malocclusion is higher in children with sucking habits than in those without the habit at 3-12 years of age. However, when children stop finger sucking before the age of 6 years, they do not have a higher percentage of malocclusion than children with no history of sucking habit. Materials and method: The frequency of thumb sucking children was studied in a prospective study of 400 children less than 13 years of age, 200 boys and 200 girls attending Ibn-alatheer pediatric hospital in Mosul city during the period between Dec 2017 and May 2018. Data were collected from the mothers. The variables considered were age, sex, residence, type of feeding, use of a pacifier, occupation of the mother, presence of thumb sucking, family history of the habit, family actions to help the child, maximum time of the habit around the day, any associated habit and any dental malocclusion in children over 6-years of age with prolonged thumb sucking. Results: It was found that the percentage of thumb sucking was less with the increase in age: 28 (28%) in children less than one years of age, 15(15%) in children between 1-4 years of age, 6(6%) in children between 4-6 years of age and 4(4%) in children above 6 years of age. It was more common among females than males in all age groups, 31 (58.4%) females were found with the habit while 22 (41.6%) males with the habit. It was more in children from urban areas 44(15%) than children from rural areas 9(8%). Thumb sucking was more common in bottle fed children 16 (16%) or on combined breast and bottle feeding 3(20%) than in children on breastfeeding only 34 (12%). A reverse association was found between thumb sucking and pacifier sucking, with pacifier only 5 (6%) children had thumb sucking, while without pacifier 48 (15%) children had thumb sucking. There was a strong family history among siblings and second degree relatives 35 (66%). There was increase in the family actions against thumb sucking with the increase of age of their children, 21(68%) of these actions were found in children above 4 years of age while only 10 (32%) family actions were found in children less than 4 years old. Although most of the family actions were traditional wrong ways with unsuccessful results 23 (47%). Maximum time of the habit around the day was at day time in infants 21 (75%), at day and night in toddlers 9(60%) and at night and sleeping time in preschool and school age children 8 (80%). Various associated habits were found with thumb sucking 11(20.7%). All school age children with prolonged thumb sucking showed class II dental malocclusion. Conclusion: The frequency of thumb sucking appears to vary by the race and culture. The habit decreases with increase in age spontaneously. Pediatrician should be more concerned about the bad effects of thumb sucking and should offer a proper advice to the parents about this habit. If necessary a pacifier may be a substitute of choice in thumb sucking because it is more readily given up at a later age than thumb sucking, with less dental malocclusion.