Despite an increasing focus on patient safety in ambulatory care, progress in understanding and reducing diagnostic errors in this setting lag behind many other safety concerns such as medication errors. To explore the extent and nature of diagnostic errors in ambulatory care, we identified five dimensions of ambulatory care from which errors may arise: (1) the provider-patient encounter, (2) performance and interpretation of diagnostic tests, (3) follow-up of patients and diagnostic test results, (4) subspecialty consultation, and (5) patients seeking care and adhering to their instruction/appointments, i.e. patient behaviors. We presented these risk domains to conference participants to elicit their views about sources of and solutions to diagnostic errors in ambulatory care. In this paper, we present a summary of discussion in each of these risk domains. Many novel themes and hypotheses for future research and interventions emerged.