The authors describe three cases of cervical radiculomyelopathy caused by calcium pyrophosphate dihydrate crystal deposition disease (CPPDcdd). Radiological investigations revealed nodular calcifications, 5 to 7 mm in diameter, in the cervical ligamentum flavum compressing the spinal cord. Light microscopic, scanning electron microscopic, and x-ray diffraction studies were performed on all three surgical specimens obtained by laminectomy. In two of the cases x-ray microanalysis and transmission electron microscope studies were also performed. This study defined the presence of two patterns of crystal deposition in the ligamentum flavum. One is a nodular deposit, in which hydroxyapatite crystals are seen in the central part of the nodules, with calcium pyrophosphate dihydrate (CPPD) being distributed thinly around them. The other pattern is a linear deposit seen in multiple ligaments and composed of pure CPPD, which causes minimal thickening of the ligaments. A transitional pattern between the two types was also observed. This study revealed details of the nodular deposition of crystals in the ligamentum flavum and demonstrates that CPPDcdd and so-called "calcification of the ligamentum flavum" are the same disease: namely, CPPDcdd. Hydroxyapatite is assumed to have been transformed from CPPD.