Although hypopituitarism is a known complication of head injury, it may be underrecognized due to its subtle clinical manifestations. The nonspecific symptoms may be masked by and may contribute to the physical and psychological sequelae of brain trauma. This study examines the prevalence of neuroendocrine abnormalities in patients rehabilitating from traumatic brain injury. Seventy adults (mean age, 31.5 +/- 1.1 yr; range, 18--58; 46 men and 24 women) with traumatic brain injury an average of 49 +/- 8 months before the study (median, 13 months) underwent a series of standard endocrine tests, including serum levels of TSH, free T(4), insulin-like growth factor I, PRL, testosterone (males), and cosyntropin stimulation. Abnormal results of these tests were followed by dynamic tests of gonadotropin, TSH, and GH secretion. Glucagon stimulation testing in 48 subjects revealed GH deficiency (peak, <3 microg/L) in 14.6%. Free T(4) (n = 6; 8.6%), TSH (n = 7; 10%), or both (n = 2; 2.9%) were low in 21.7%, whereas 87% had both TSH and free T(4) below the midnormal level. Basal morning cortisol was below normal in 45.7% of subjects, whereas cosyntropin-stimulated levels were insufficient (peak, <500 nmol/L) in 7.1%. Hypogonadism and hyperprolactinemia were uncommon. In summary, pituitary hormone deficiencies were identified in a substantial proportion of patients with previous brain injury. GH deficiency, found in 15% by glucagon stimulation testing, may compound the physical and psychological complications of traumatic brain injury and interfere with rehabilitation.