Background: The lightness of teeth and the distances of the upper and lower lip from the maxillary cervical and incisal lines are factors that correlate with smile attractiveness. Purpose: This study investigates the degree of association of the above factors with smile attractiveness and evaluates the possible effect of evaluators' gender, age, occupation, and education level on the perception of smile attractiveness. Materials and methods: An almost perfect smile of an adult Caucasian female was altered to create various smile images with differences in lightness of teeth and upper and lower lip positions. The images were randomly assembled in three slides of four, seven, and five images each and presented to 130 participants to evaluate the most attractive smile (MAS) and the least attractive smile (LAS). Data collected were analyzed for differences between gender, age, occupation, and education level as regards the evaluation of the MAS and LAS using the chi-square test with a significance level of α = 0.05. Results: Statistical analysis showed that the smile images in L1 and L2 were equally considered to be the most attractive smiles. The chi-square test indicated no differences between all groups (P > 0.05). Percentages for the most attractive smiles for the lower lip positions were almost equal for most positions of the upper lip, with differences only between age groups (P > 0.05). The least attractive smiles were those with the upper lip position at 3 mm above the cervical line, with differences only between occupation groups (P 0.001). Conclusion: The results of this study indicate that lightness of teeth positively affects smile attractiveness. Lower lip positions with a distance of 0 to 1 mm from the maxillary incisal line are considered more attractive. Upper lip distances were strongly associated with smile attractiveness. Gender, occupation, and education level did not differently affect the perception of attractiveness due to lower lip positions, but age did.