We studied the growth of 89 patients who were long-term survivors of childhood leukemia and lymphoma. Eight patients with CNS relapse had a greater decrease in height standard deviation score (SDS) after the relapse than 81 patients without CNS relapse (p < 0.0001). Two patients who received cranial irradiation when they were younger than 2 years of age demonstrated a marked de-crease in height SDS more than 3.0 SD. Five patients appeared to have a decline in height SDS before their CNS relapse. There were no apparent changes in the weight of patients with or without CNS relapse. In endocrine studies, all eight patients with CNS relapse failed to show the normal growth hormone (GH) response to arginine, GH-releasing factor, and glucagon-propranolol tests, while spontaneous GH secretion during sleep was normal. Magnetic resonance imaging (MRI) revealed small pituitary glands in seven patients with CNS relapse. These findings suggest that in leukemia and lymphoma patients with CNS relapse, GH secretion is impaired at the hypothalamic level, resulting in a secondary atrophy of the pituitary gland. The MRI together with selected endocrinologic tests may help to clarify the mechanism of growth impairment in such patients. A decline in height SDS in each patient may be a useful marker for predicting a CNS relapse in a child with leukemia or lymphoma.