Randomized controlled trials remain the gold standard study design and yield the highest level of scientific credence. However, recognition of the limitations of the randomized controlled trial is important. This review highlights 10 potentially problematic areas one should carefully assess when performing or reading an article reporting the results of a randomized controlled trial, problematic areas that can affect the outcome of the trial and therefore mislead the reader. These areas include ethical issues, eligibility criteria, masking (blinding), randomization, analytic methods, the selection of subjects for the interventional and comparison groups, selection of end points, and the interpretation of the results. Each of these is discussed, and examples of published articles are used to highlight the main points. ©2006 the American College of Clinical Pharmacology.