Background: A reliable means of treating hyper-triglyceridemia is the use of large doses of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Modest levels of EPA and DHA may be obtained from food, particularly fatty fish. Objectives: This article is intended to review clinically relevant differences between dietary-supplement omega-3 fatty acids and prescription omega-3-acid ethyl esters (P-OM3). Methods: PubMed and the Food and Drug Administration (FDA) Website were searched for articles published between 1995 and 2007 that contained the terms fish oil, fatty acids, n-3 fatty acids, omega fatty acids, docosahexaenoic acid, or eicosapentaenoic acid. Articles discussing sources, recommended intake, and differences among various formulations of omega-3 fatty acids were selected for review. A limitation to this review is the lack of head-to-head clinical trials using P-OM3 and dietary-supplement omega-3 fatty acids. Results: Many types of nonprescription dietary supplements of omega-3 fatty acids are available; however, the efficacy, quality, and safety of these products are open to question because they are not regulated by the same standards as pharmaceutical agents. P-OM3 is the only omega-3 fatty acid product (Omacor* capsules) approved by the US FDA available in the United States as an adjunct to diet to reduce very high (>= 500 mg/dL) triglyceride levels in adult patients. Conclusions: P-OM3 can be used with confidence by practitioners who want to provide therapeutic doses of omega-3 fatty acids in a preparation that has been documented to be both safe and effective.