Patients with acromegaly have characteristic clinical features caused by soft tissue overgrowth. The most common cause of acromegaly is a growth hormone-secreting adenoma of the anterior pituitary. Both somatic and metabolic features of acromegaly are due to excess growth hormone (GH) secretion and high serum concentrations of insulin-like growth factor-I (IGF-I). Here we present a case of "pseudoacromegaly" with an acromegaloid phenotype, insulin resistance, history of adenomatous colonic polyp, and suppressed IGF-I levels. Patients with this rare condition are likely to have a selective post-receptor defect of insulin signalling, leading to the impairment of metabolic but preservation of mitogenic signalling. Endocrinologists should consider this diagnosis when assessing patients with clinical features of acromegaly and insulin resistance, in the absence of elevated levels of GH and IGF-I.