Introduction: Oral parafunctions are considered one of the causal factors of temporomandibular disorders and have gained importance in recent decades, especially in child and young populations, although evidence is scarce in the preschool children and nonexistent in the indigenous groups. The objectives of this study were to determine the prevalence of oral parafunctions and the presence of caries in pehuenche preschool children, from Alto Biobio commune, the poorest one in Chile, as well as the possible association of the ethnodemographic and the socioeconomic characteristics. Methods: A sample comprised 71 children from 2 to 5 years attending kindergarten; the permission of local authorities and the informed consent of parents were granted. Socio-ethno-demographic variables, decay presence in primary teeth (dmft index) according to WHO criteria and the presence of 8 oral parafunctions: finger sucking, object sucking, sucking on bottle, pacifier and lip sucking, tongue thrust, onychophagia and mouth breathing, were all evaluated through a survey made to kindergarten educators. Results: Of the studied children, 9.86% were caries-free and the dmft index was 6.83 ± 4.65, increasing with the age, hence, it was 2.8 at age 2 and 8.23 at age 5. Oral parafunctions average was 1.73 ± 1.06 per child, significantly higher in women, pehuenches and extremely poor children. Prevalence for any of the 8 oral parafunctions was 90.86% and for those associated with non-nutritive sucking was 77.46%. The most prevalent were bottle and labial sucking (26.76%), onychophagia (29.58%) and finger sucking (47.89%). Conclusions: Decay presence in these preschool children is very high, whereas the prevalence of oral parafunctions is similar to that of other populations, affecting more children in extreme poverty setting and pehuenches. All this is possibly related to the social vulnerability of the commune. These results highlighted the urgent need of implementing preventive, promotional and therapeutic strategies in this population.