A case of gross macroscopic gelatinous transformation of bone marrow associated with prolonged malabsorption due to celiac disease is reported. Histochemical studies support the view that the extracellular myxoid tissue is composed predominantly of acid mucopolysaccharides, and electron microscopy shows extracellular fine fibrillar and granular material. The replacement of marrow in this condition is histochemically different from serous fat atrophy occurring in epicardial fat, and it is suggested that it results from an increase in normal ground substance. It must be differentiated from metastatic signet ring adenocarcinoma.