Objective: To evaluate the effect of premature delivery and birth weight (BW) on primary tooth eruption. Methods: A total of 2,230 children aged 3 to 36 months from urban and rural areas in Beijing, China, were classified for analysis by gestational age at delivery (89 preterm and 2,141 full term) and BW (low, normal and high). The tooth eruption status of these children was examined and recorded every 3 months. Results: The timing of first primary tooth eruption was significantly delayed in preterm infants (8.4 months versus 7.3 months for full term; P 0.05). Furthermore, the number of teeth was significantly less for the preterm and low-BW groups at 12 to 18 and 24 to 30 months, but the number of teeth caught up with normal-BW children by 30 to 36 months. In contrast, the time of first tooth eruption of high-BW children was earlier, while the erupted teeth at each month range was more than the normal-BW group. This research also demonstrated a negative correlation (r = -0.202; P = 0.009) between the time of first primary tooth eruption and BW as well as a positive correlation between the number of erupted teeth and BW. Conclusion: Premature delivery and BW were the influencing factors for the timing of primary tooth eruption in children from Beijing, China. Recommendations for feeding habits and oral healthcare implementation may vary according to different primary tooth eruption status among individuals. Keywords: tooth eruption, primary teeth, premature delivery, birth weight (BW)