OBJECTIVE: Familial glucocorticoid deficiency (FGD) has frequently been associated with tall stature in affected individuals. The clinical, biochemical and genetic features of five such patients were studied with the aim of clarifying the underlying mechanisms of excessive growth in these patients. PATIENTS AND METHODS: Five patients with a clinical diagnosis of FGD are described in whom the disorder resulted from a variety of novel or previously described missense or nonsense mutations of the ACTH receptor (MC2-R). All patients demostrated excessive linear growth over that predicted from parental indices and increased head circumference. RESULTS: Growth hormone and IGF-I-values were normal. Growth charts suggest that the excessive growth is reduced to normal following the introduction of glucocorticoid replacement. A characteristic facial appearance including hypertelorism, marked epicanthic folds and prominent frontal bossing was noted. CONCLUSIONS: These findings indicate that ACTH resistance resulting from a defective ACTH receptor may be associated with abnormalities of cartilage and/or bone growth independently of the GH-IGF-I axis, but probably dependent on ACTH actions through other melanocortin receptors.