Medical education in the US has adapted to the shift of patient care from hospital to ambulatory settings by developing educational opportunities in outpatient settings. Faculty development efforts must acknowledge learners' perspectives to be effective in improving teaching and learning. Clinics provide important and unique learning opportunities, but also present different challenges for preceptors (i.e., physician teachers) and learners. Multiple studies have identified characteristics of effective preceptors of ambulatory care medicine. However, most of these studies were conducted among residents or students with clinical experience. To investigate preclinical, second-year medical students' perceptions of preceptor quality, we conducted an exploratory qualitative study using analysis of student learning journals. The purposive sample included 120 medical students in a private, Midwestern medical school in the United States. Learning journals of 110 students for two semesters were reviewed. Five attributes of an effective preceptor emerged: (1) Demonstrates professional expertise (2) Actively engages students in learning (3) Creates a positive environment for teaching and learning (4) Demonstrates collegiality and professionalism (5) Discusses career-related topics and concerns. Our findings suggest preclinical learners often begin initial clinical experiences with sophisticated definitions of professional expertise, and hold specific expectations for professionalism. These are based on previous coursework and personal experience. These expectations influence their perceptions of effective preceptors and learning experiences. Early clinical experiences can also influence perceptions about career and specialty choice. Improving our understanding of preclinical learners' perceptions of preceptor quality will improve the efficacy of faculty development efforts and learning experiences.