The purpose of this perspective is to describe an approach to teaching diagnostic reasoning using a Web-based course. To elucidate this we describe how we match the learning needs of practicing clinicians in the realm of diagnostic reasoning with specific teaching methods used in an online course format. We use 3 principles of teaching and learning diagnostic reasoning skills to frame the discussion: 1) ready access to information 2) active participation of all students; and 3) self appraisal and metacognition. These three principles guided the method of developing and conducting this online course called: Diagnostic Screening for Physical Therapists: When to Treat? When to Refer? Experienced physical therapists are adult learners. They pursue their own areas of interest; find their own resources for learning, and pace themselves according to their own learnging needs. The Web-based format lends itself to this type of teaching and learning, using Web-based access to information, and collaborative learning groups engaged in constructing new knowledge by integrating what they have stored in memory with new insights they gain from others. Adult learners come to the course with knowledge and inferences arrived at by their own clinical experiences. By interacting with other students and teachers, they engage in an analytical approach to solving patient problems which requires them to reflect on their own practice and share their thinking strategies with others. This enables them to learn more deeply than simply memorizing facts, or strategically trying to perform all of the course requirements as quickly as possible. They learn by solving real clinical problems using cases that present confusing and complex signs and symptoms and by doing this in an ongoing threaded discussion with fellow physical therapists. The online format permits them flexibility of scheduling and much more time to engage with each other in discussion than a traditional classroom would provide.