Many clinicians base their treatment choices on trial outcomes. To determine if clinical trial results apply to the general patient population, several factors need to be considered. The exclusion and inclusion of patients in a trial may present selection bias. Adherence to therapy in trials often varies widely compared with adherence seen in clinical practice. Endpoints used in trials compared with endpoints used in practice are not always comparable. The performance and publication of clinical trials can be affected by investigator or publication bias. Finally, reporting of data as mean values may not always relate to the outcome in individual patients. By understanding some of these issues, clinicians can begin to better relate trial results with patient treatment options.