Pediatric psychopharmacology is a relatively new science. Although the use of psychotropic medications in children has risen in the past decade, there are few standard treatments for serious psychiatric or developmental disorders of childhood. The relative absence of standard treatments is further complicated by the fact that many of the agents used in pediatric psychopharmacology have been adapted from other fields. Therefore, investigators have a responsibility to make incremental progress from concept through pilot studies and large-scale, multisite efficacy and safety (...) trials. Thus, although there is a pressing need to conduct medication trials that can guide clinical practice, there are scientific and ethical considerations to bear in mind when designing clinical trials in pediatric psychopharmacology. This article reviews essential ethical and scientific issues that are relevant to designing clinical trials in children with psychiatric and developmental disorders. Using examples from recently published literature, the article describes the challenges and pitfalls of various clinical trial study designs. The application of sound ethical and scientific principles is necessary to ensure that clinical trials are properly conducted and to guard against ambiguous results that can not guide practice. (shrink)