Objectives: The aim of this study is to establish accurate diagnostic treatment decision threshold of proximal carious lesion in relation to the angle and depth of radiolucency in radiographic image in Saudi population. Methods: Bitewing x-rays were examined to detect the level of lesion depth and angle. Criteria for lesion depth were divided into four categories (E1, E2, DEJ & D). Radiolucincies in the bitewing radiograph extending less than or equal to outer half of enamel(E1), more than the inner half of enamel and before DEJ(E2), at the Dentinoenamel junction(DEJ), less than or equal to the outer half of dentin(D). Angle and Depth were also measured using SIDEXIS XG software (Sirona, Bensheim, Germany). Clinically, cavitation was evaluated at proximal tooth surfaces directly after the extraction of the adjacent tooth or missing proximal contact with the adjacent tooth due to several different indications (Decayed, orthodontic reasons, etc.). Independent T-test was used to correlate between (lesion depth & angle of radiolucency) with clinical cavitation. Chi-square test was used to correlate lesion depth of four categories with clinical cavitation. Results: 116 approximal surfaces with (age mean=31 years old) had (41 cavitated, 75 non-cavitated) proximal surfaces. Premolar 56.9% and Molar 43.1%. There is significant relationship between cavitation and increasing depth in proximal surface that gave P-value= (0.000). A significant relationship was found between clinical cavitation and the angle of approximal enamel surface with P-value = (0.024). Conclusion: With limitations in this study, dentists should be aware of contrast of the approximal lesion angle (determined by three points, most coronal radiolucent point, the deepest axial point and the most apical radiolucent point) of bitewing x-rays to evaluate operative intervention in proximal surface. The more increase in angle the less tendency toward cavitation.