The Roentgen manifestations in 75 patients with hypercalcemia have recently been reviewed at The John Hopkins Hospital. This series represents patients studied by the Department of Endocrinology and also patients with a high serum calcium reported by the Chemistry Laboratory during the year 1952. Only cases for which sufficient clinical information, satisfactory films, and conclusive evidence of hypercalcemia were available were included. The distribution of cases according to etiology with the range of serum calcium determinations for each group is presented in Table I. The roentgenologic skeletal findings fell into five categories: (a) focal and disseminated lesions, (b) malacic lesions, (c) porosis, (d) changes characteristic of Paget's disease, and (e) absence of roentgen skeletal abnormalities. Focal and Disseminated Lesions Multiple osteolytic foci, varying in size and dissemination and without surrounding bony reaction, were the predominant feature in this series of patients. All of these lesions proved to be of neoplastic origin. Widely disseminated destructive changes were most frequent in multiple myeloma (Fig. 2) and less frequent in other malignant neoplasms, such as carcinoma of the breast. In a few cases of breast cancer, osteoblastic metastases were observed. Of some interest is the occurrence of high serum calcium in such a wide selection of neoplastic diseases. In addition to those mentioned in the preceding paragraph, 1 case each was encountered of melanosarcoma, Ewing's tumor, carcinoma of the penis, carcinoma of the gallbladder, undifferentiated carcinomatosis, undifferentiated lymphoid disease, and chronic lymphatic leukemia. (Two patients with multiple myeloma and 6 with carcinoma of the breast received hormonal therapy which probably influenced the serum calcium levels. This influence is not felt to be the important factor, since most of these patients had hypercalcemia before treatment was started.) Malacia Generalized decreased bone density with a coarsened fibrous effect and an indistinct fuzzy appearance of the cortices constitutes the essence of the roentgen manifestations of the malade group (Fig. 3). In more detail, the changes are as shown in Table II. From a roentgen point of view, the differential diagnosis of malacic bone disease should include renal and nutritional causes of rickets as well as hyperparathyroidism (Table III). However, due to the fact that in each of the rachitic diseases the serum calcium is normal or reduced, the presence of a high serum calcium narrows the possibilities to hyperparathyroidism. In this series when the bones were observed to fulfill the criteria of the malacic group, the diagnosis proved to be exclusively hyperparathyroidism, except for 5 cases in which a final clinical diagnosis has not yet been established.