Is the diagnostic ability of medical students--as appraised by the Diagnostic Thinking Inventory (DTI) --influenced by the learners' characteristics, or the way they acquired basic knowledge? This question was explored in a 4-year consecutive sampling of clinical clerkship students. DTI inventory scores (flexibility in thinking and structure in memory), learners' characteristics (learning style, self-confidence as a learner, and motivation to learn), together with knowledge scores (grade-point) average and problem-solving test) were measured and analysed for their relationships and the differences between groups. Results revealed that higher scores of the DTI measures were associated with students' high self-confidence, high motivation to learn, and abstract learning types. Correlation coefficients showed significant relationships between the DTI scores and both knowledge measures. In addition, t-tests showed that students with an integrated teaching background and problem-based learning (PBL) experience obtained significantly higher scores for structure in memory. The findings suggest that the inventory scores are sensitive to both cognitive and non-cognitive factors. The inventory may be useful detecting subtle influences on diagnostic ability differentiation in medical students.