Introduction: Judgment in the face of uncertainty is an important dimension of expertise and clinical competence. However, it is challenging to conceive continuing professional development (CPD) initiatives aimed at helping physicians enhance their clinical judgment skills in ill-defined situations. We present an online script concordance-based CPD program (the "Practicum Script Concordance Test", copyright [C]2006 by Practicum Foundation), a tool that can be used to support health professionals in the development of their reflective clinical reasoning ability. We describe the rationale and principles and report on the implementation of 2 online programs based on this new CPD initiative. Method: The Practicum Script Concordance Test program consists of daily testing and feedback over the course of a year using SCT items. Feedback is both global (eg, health professionals are told their cumulative mean score) and specific (eg, they can view the expert panel's responses together with their justifications for their answers). Participants have the option of contacting a personal tutor, to whom they can send questions. Data regarding feasibility, participation, and acceptability were collected. Results: Initial implementation took place in Mexico where 1901 physicians (1349 paediatricians, 552 cardiologists) were enrolled in Practicum programs. Around 70% of those enrolled pursued the program and were very satisfied with its format and content. The online format was an important factor in the development and maintenance of the programs. Dropouts had issues with the SCT concept and the time required to participate. Discussion: The on-line Practicum Script Concordance Test program was designed to foster expertise development based on practice, reflection and feedback. Although further research is needed to examine its impact physicians' practice and ultimately on patient outcomes, it is an original and promising development in CPD. (Contains 2 tables and 3 figures.)