In order to describe the signs of acromegaly in cats, a case-control study was done based on computed tomography (CT) scans of the heads of 68 cats with hypersomatotropism and 36 control cats. All cats with a diagnosis of hypersomatotropism had diabetes mellitus, serum insulin-like growth factor-1 >1000 ng/ml and a pituitary mass. Measurements of bones and soft tissues were done by two independent observers without knowledge of the diagnosis. Pituitary masses were identified in CT images of 64 (94%) cats with hypersomatotropism. Analysis of variance found a moderate effect of gender on the size of bones and a large effect of hypersomatotropism on the size of bones and thickness of soft tissues. In cats with hypersomatotropism the frontal and parietal bones were, on average, 0.8 mm thicker (P <0.001); the distance between the zygomatic arches was, on average, 5.4 mm greater (P <0.001); and the mandibular rami were, on average, 1.1 mm thicker (P <0.001) than in control cats. The skin and subcutis dorsal to the frontal bone were, on average, 0.4 mm thicker (P = 0.001); lateral to the zygomatic arch were, on average, 0.7 mm thicker (P <0.001); and ventral to the mandibular rami were, on average, 1.1 mm thicker (P = 0.002) in cats with hypersomatotropism than in control cats. The cross-sectional area of the nasopharynx was, on average, 11.1 mm(2) smaller in cats with hypersomatotropism than in control cats (P = 0.02). Prognathia inferior and signs of temporomandibular joint malformation were both observed more frequently in cats with hypersomatotropism than in control cats (P = 0.03). Overall, differences between affected and unaffected cats were small. Recognising feline acromegaly on the basis of facial features is difficult.