A number of factors have contributed to the relatively rapid development and growth of the Objective Structured Clinical Examination (OSCA) as a viable and popular assessment tool. Among these was an increased need, expressed both by training institutions and certifying and licensing bodies, for valid performance-based assessment approaches. That this need became apparent at a time when concern and interest in performance-based assessment in education generally was growing, was fortuitous and contributed to the developments in medical education. In medical education important consequences were the growing interest and expertise in two distinct areas, the psychometrics of performance assessment and the use of standardized (simulated) patients in the teaching and assessment of clinical skills. Collaboration between people working in these two areas greatly facilitated the rapid development and refinement of the OSCA. Currently, there appears to be general acceptance of the legitimacy of this assessment approach. Research now seems to be directed at resolving remaining important technical problems (e.g. standard setting); the design and implementation of large scale national and regional certifying and licensing examinations are the primary current development challenges. There is a large and still growing body of related literature and many presentations about this assessment approach are given at medical education conferences.