Despite increased awareness about patient safety and quality of care, errors and adverse outcomes occur frequently in clinical practice. An estimated 10% of the U.S. hospital patients in 2010 suffered injuries caused by medical errors; the most common medical errors were medication errors, which accounted for more than 50% of all medical errors. Work-related stress (WRS) has been shown to be associated with medication errors for health care professionals (HCP) but the specific types of stressors and their effect on the level of medication errors have not been studied. The purpose of this quantitative correlational study was to examine the relationship between the overall level and sources of WRS using the Job Stress Scale on the level of medication errors for a group of 269 HCPs working at King Abdul-Aziz Hospital (KAH) in Saudi Arabia (SA). The theoretical framework for this research was the Donabedian Patient Safety model, which relates healthcare quality to personal, environmental, and organizational factors. Binary logistic regression analyses were employed to test the hypotheses. The result indicated there was no relationship between overall levels of stress and medication errors. However, disruption to home life, excessive workload, and night/weekend call duties were associated with a significant increase in the medication error rate while pressure to meet deadlines and difficulties with colleagues were associated with a significant decrease in the medication error rate. Understanding the impact of work-related sources of stress on medication errors by SA HCPs may lead to interventions reduce medication errors and improve patient care.