Background: Abbreviations which resulted in harmful patient errors or death are termed dangerous abbreviations. These abbreviations were included in The Joint Commission “Do Not Use" list of abbreviations launched in May 2005. Objectives: The aim of the present study is to assess physicians' and nurses' use of unapproved and dangerous abbreviations and to explore physicians' and nurses' opinion regarding the use of these abbreviations. Methods: The study was conducted in a Joint Commission International (JCI) accredited hospital in Eastern Saudi Arabia. Two study designs were used: retrospective descriptive and cross-sectional descriptive. Data were collected through reviewing 384 paper records and distributing a questionnaire to a random sample of 58 physicians and nurses. Results: The study revealed that the average number of dangerous abbreviations per record was 2.2 while the average number of unapproved abbreviations per record was 1.96. The most frequent dangerous abbreviation reported in the present study was Discharge/Discontinue D/C accounting for 73% of the total identified dangerous abbreviations for both physicians and nurses. The ability of physicians and nurses to correctly identify the meaning of the most commonly used dangerous abbreviation and unapproved abbreviation ranged between 37.9% and 69.0%. Conclusions: The study revealed high use of dangerous and unapproved abbreviations at the study hospital. Few dangerous abbreviations constitute the majority of identified abbreviations. A quality improvement intervention needs to be instituted to reduce abbreviation use at the study hospital.