Patient safety is a new healthcare discipline that emphasizes the reporting, analysis, and prevention of medical error that often leads to adverse healthcare events. According to research, 60 to 80% of all identified errors could be considered as preventable, making patient safety an area of growing interest both in public as well as among health care professionals. Most experience of medical error has been gained from the secondary care environment, but little is known about the situation in primary care, where the majority of patient contacts with health care providers occurs. Four dimensions of patient safety issues have been identified in primary health care: diagnosis, prescribing, communication between patients and providers of care, and organisational issues. However, prevalence studies show that diagnostic errors predominate in general practice settings: of all adverse incidents reported in the primary care setting, 28% to 78% are related to the problems with diagnosis. Prompt diagnosis of poorly differentiated and potentially serious disease represents one of the core competencies of family physicians. Diagnosis is central to the family physcian’s role and diagnostic error has the potential for the most serious consequences for patients, since all management decisions, including referrals and treatment, are based on diagnosis. Studies have begun to identify the root causes that contribute to diagnostic error. These causes include either one or more of the following: clinician cognitive factors and systems factors. Understanding the root causes that contribute to diagnostic error can bring substantial help in preventing future adverse medical events.