The primary care clerkship (PCC) at Harvard Medical School was established in 1997. The goals are to provide students with longitudinal experiences with patients and to include modern themes in the curriculum: managing illness and clinical relationships over time; finding the best available answers to clinical questions; preventing illness and promoting health; dealing with clinical uncertainty; getting the best outcomes with available resources; working in a health care team; and sharing decision making with patients. The PCC, a required course in the clinical years, meets one afternoon a week for nine months. Students spend three afternoons per month in primary care practices, where they see three to five patients per session and follow at least one patient ("longitudinal patient") over time. Classroom sessions, in both large- and small-group formats, promote a common educational philosophy and experience, and reinforce habits of problem-based learning established in the preclinical years. The students rated 74% of their preceptors excellent, especially praising their ability to facilitate and support good interpersonal relationships with patients, their ability to encourage students' independent evaluation of patients (as opposed to shadowing), and their enthusiasm for teaching. Students saw their longitudinal patients a mean of 4.8 times; 83% saw their patients at least three times. The PCC complements the curriculum of block clerkships in hospitals, and because the two are offered concurrently, students are required to come to terms with two substantially different cultures within medicine. Other medical schools are beginning to develop longitudinal clerkships to ensure that students have essential educational experiences that are difficult to achieve in block, hospital-based clerkships.