Purpose: To evaluate the association between the contact areas of primary molar teeth and approximal caries after three years of observation. Methods: This prospective cohort study included 1,119 caries-free children, aged three to four years, from Puducherry, India. At base- line, 4,476 contacts were assessed using the OXIS criteria, which denotes O for open contact and X, I, and S for closed contacts. X contact represents a point contact, I is a straight contact, and S is a curved contact. Two calibrated dentists measured dental caries at one-year intervals following the International Caries Detection and Assessment System for three years. Poisson regression analysis with a multilevel approach was used to determine the association between contact type and approximal caries. Results: Of 3,848 contacts observed at the end of three years, 499 (13 percent) were carious. The adjusted analysis revealed a significant association between contact type and approximal caries (P<0.05). The risk ratios for the development of approximal caries were 2.3 for X-type contacts (0.5 to 11.4, P=0.307), 12.7 for I-type (4.1 to 39.6, P<0.05), and 22.5 for S-type (7.2 to 70.6, P<0.05) when compared with O-type. Conclusions: Compelling evidence suggests that variations in contacts between teeth are significant in the development of approximal caries. The S-type contact is the most susceptible to approximal caries, followed by the I-type.