Abstract An initial clinical suspicion of acromegaly has traditionally been the necessary first step toward making the diagnosis. However, because of the typically insidious nature of the clinical syndrome, acromegaly is usually underrecognized with a long delay from disease onset to diagnosis. Some patients present with few or none of the typical clinical manifestations. Therefore, the first pitfall to avoid in diagnosing acromegaly is to dismiss the diagnosis in a patient without obvious clinical signs or symptoms. Improvements in biochemical testing are now available that may help lead to the detection of this disease in its earlier stages. Biochemical testing consists of evaluation of both the degree of growth hormone (GH) suppression after oral glucose administration (OGTT) and levels of the GH-dependent peptide, insulin-like growth factor I (IGF-I). Potential pitfalls in the biochemical assessment of acromegaly can arise from misinterpretation of the results of GH testing, which can result from failure to recognize that older GH criteria for diagnosis are no longer applicable to interpretation of GH levels measured with modern sensitive and specific GH assays. Suppression of GH to less than 1.0 μg/L during an oral glucose tolerance test (OGTT) may help exclude acromegaly when GH is measured with some current commercially available assays, but with the use of highly sensitive assays, a fall of GH to less than 1.0 μg/L during an OGTT does not necessarily exclude the disease. Failure of GH to suppress, however, may occur in some healthy subjects, in particular young healthy women and adolescents. Clinical settings other than acromegaly can also be associated with failure of normal GH suppression such as chronic renal insufficiency, liver failure, active hepatitis, hyperthyroidism, diabetes mellitus, anorexia nervosa, and other forms of malnutrition. An essential part of the biochemical diagnosis of acromegaly is also documentation of an elevated serum IGF-I level. When measured properly and compared with a well-characterized, age-adjusted normative database, elevation of the serum IGF-I level is a sensitive and specific indicator for the presence of acromegaly. Interpretation of IGF-I levels must consider important regulators of IGF-I production such as nutritional status and age that significantly influence serum levels of IGF-I. Chronic and critical illness, including liver disease, renal failure, diabetes mellitus, and thyroid disease, may also alter serum IGF-I levels. An increased IGF-I is almost always specific for acromegaly, but in 2 important instances, pregnancy and adolescence, IGF-I may be increased without acromegaly. Greater awareness of limitations of current GH and IGF-I assays as well as interpretation of GH testing in conjunction with serum IGF-I levels and within the clinical context of the patient being assessed will help to avoid these potential pitfalls to the diagnostic assessment of acromegaly.