A rare endocrine disease characterized by unusually tall stature (with rapid growth velocity), occurring before closure of the epiphyseal growth plates, due to excessive growth hormone (GH) caused by a GH-secreting pituitary tumor or from pituitary hyperplasia. Additional associated features may include pubertal delay, visual defects, headache, excessive appetite, hyperhidrosis and menstrual irregularity, as well as variable manifestations characteristic of acromegaly, such as prognathism, coarse facial features and large hands/feet in adolescents.

Bizygomatic (upper face) and bigonial (lower face) width are both more than 2 standard deviations below the mean (objective); or, an apparent reduction in the width of the upper and lower face (subjective).