To evaluate the ability of dentists and dental students to detect caries by using the International Caries Detection and Assessment System (ICDAS). Materials and Methods: A cross-sectional study was conducted in Riyadh city and in the College of Dentistry at King Saud University (KSU) in Saudi Arabia. The study sample included a cluster sampling of 50 private clinics (100 dentists) and all 3rd-, 4th-, and 5th-year students (393 students). Data were collected using an electronic questionnaire. The ability score of detecting caries for each group was identified by calculating the mean percentages of the score. The data were entered into SPSS Version 20. One-way ANOVA was used for comparing quantitative data. Results: The overall response rate of the survey was 64.5% (318/493). A total of 62.6% (199) of respondents know about ICDAS. All groups had difficulty assessing the activity of caries in Code 2. There were significant differences among all groups in the ability to detect caries (P-value: 0:00). Moreover, 4th-and 5th-year students had the highest mean of percentage ability score (53.8% and 57.6%, respectively) to detect caries using ICDAS compared to 3rd-year students and general practitioners (38.6% and 38.7%, respectively). Conclusion:Overall, detection of early dental caries limited to enamel was confusing and difficult. The abilities of dentists and dental students to detect caries using ICDAS were low and require improvement by continuing further clinical training.