Purpose: To longitudinally evaluate oral habits and their effects on the developing occlusion in Nigerian children. Materials and Methods: A longitudinal epidemiological survey of 145 3- to 5-year-old children in a pre-primary section of a primary school near the Dental Centre, University College Hospital, Ibadan, Nigeria. The children at the first examination (Time 1) were screened for oral habits. They were then followed up and those located 4 years later were reassessed for oral habits (Time 2) in the primary school section of the same establishment. Only subjects who were actively engaged in non-nutritive sucking were coded positive. The occlusal features at Time 1 were recorded according to Foster and Hamilton, whereas at Time 2 the molar relationship was based on Angle's classification. Both descriptive statistics and Pearson correlation coefficient were used in the data analysis. Results: At Time 1, only 5 (3.4%) children in the original sample size were non-nutritive suckers, whereas at Time 2, 19 (31%) of the final sample size were involved in oral habits, with three of the initial children still involved, giving an incidence rate of 26.2%. Of the initial five non-nutritive suckers at Time 1, four were digit suckers and one a lip sucker. At Time 2, eight children were involved in digit sucking; seven in tongue thrusting/sucking, two in both digit and tongue sucking and two were nail biters. Five (4.5%) of 11 subjects with a Class 1 molar relationship at Time 1 had a Class II molar relationship at Time 2. The correlations between the oral habits at the two stages of occlusal development and anterior open bite were statistically significant (P 0.01). Conclusions: There was an increase in the number of children involved in oral habits at the early mixed dentition stage with significant correlations between oral habits and anterior open bite as well as a higher tendency towards Class II molar relationship for those with initial Class I. Keywords: Nigerian children, occlusal development, oral habits