Background: Despite being a mandated, foundational value in healthcare, research on compassion remains limited. Studying the individual, patient, clinical, and contextual factors that interfere with compassion--the "barriers"--may clarify our understanding of the origins of compassion and identify potential targets for improving patient-centred care. Studies of the related construct of empathy have suggested that medical students report declines with increasing clinical experience. In contrast, when comparing physicians with medical students, increased clinical experience predicts lower barriers to compassion. Whether--and how--a similar experience-related decline in the factors that interfere with compassion occurs across medical training remains unknown. Aims: To describe how the barriers to compassion vary across clinical training in medical students. Method: New Zealand medical students (N = 351) in their clinical years (Years 4-6) completed measures of the Barriers to Physician Compassion (BPCQ) and potential covariates such as demographics, work burden factors, and dispositional factors. The BPCQ indexes the extent to which barriers in four domains (individual, patient, clinical, and contextual) interfere with a physician/student's compassion towards patients. Analyses of variance and regression analyses were used to explore the effect of year level on the four types of barriers. Results: Year 4 students reported slightly lower student-related, environmental and patient/family-related (but not clinical) barriers than Year 6 students (effect size: [omega][superscript 2] < 0.05); all barriers increased comparably across training. Controlling for relevant confounds, regression analyses confirmed that lower year level predicted lower barriers to compassion. Higher self-compassion, but not gender, predicted lower barriers. Conclusions: In extending studies of empathy decline, this report suggests that students experience higher barriers to compassion as clinical training progresses. This is in contrast to existing studies contrasting physicians with medical students, where greater experience was associated with lower perceived barriers to compassion. Self-compassion may offset increases in barriers to care.