The purpose of this study was to determine the association between the duration of nutritive and nonnutritive sucking behaviors and various occlusal characteristics in the primary dentition. Sucking behavior data were collected on 372 children followed longitudinally from birth by using periodic questionnaires completed by parents. Study models were obtained from the children at 4 to 5 years of age and assessed for posterior crossbite, anterior open bite, and overjet. Dental arch parameters including arch widths, arch lengths, and arch depths were measured directly from the models. The subjects were grouped according to type of habit (pacifier or digit) and duration of nonnutritive sucking behaviors (less than 12, 12 to 24, 24 to 36, 36 to 48, and more than 48 months). Children with nonnutritive sucking of less than 12 months were further grouped according to the duration of breast-feeding. The dental arch and the occlusal characteristics were then compared among these groups. The results indicated no relationship between duration of breast-feeding during the first year of life and any dental arch or occlusal parameters. The study found that prolonged pacifier habits resulted in changes to the dental arches and the occlusal parameters that were different from the effects of digit sucking. In addition, some changes in the dental arch parameters and occlusal characteristics (eg, prevalence of posterior crossbite and increased amount of overjet) persisted well beyond the cessation of the pacifier or digit habit. Although further study is needed to determine the effects of nonnutritive sucking behavior in the mixed dentition, the results suggest that current recommendations for discontinuing these habits may not be optimal in preventing habit-related malocclusions.