In summary, the differential diagnosis of gigantism includes a significant number of heterogeneous disorders exhibiting a vast array of clinical and genetic features. In most cases, the history, physical examination and adjunctive biochemical and/or molecular genetic testing will ultimately reveal the likely diagnosis. Albeit rare, diseases resulting in gigantism afford the unique opportunity for a glimpse into the complex mechanisms of growth regulation. Thus, continued clinical and scientific investigation will enhance not only individual patient care, but also collective insight into the intricacies of the fundamental processes of human growth.