OBJECTIVE: Both of ossification of posterior longitudinal ligament (OPLL) and cervical spondylotic myelopathy (CSM) could be treated by cervical laminoplasty. In this study we compared long-term clinical and radiological outcomes in these two disease entities, treated with modified midline splitting laminoplasty (MSL). METHODS: We retrospectively analyzed the outcomes of 21 consecutive cervical myelopathy patients (13 OPLL and 8 CSM) who underwent modified MSL between 2004 and 2008. The mean follow-up duration was 49.5 months. The clinical outcomes were evaluated by the Japanese Orthopedic Association (JOA) score and the radiologic outcomes included the change of cervical lordosis, range of motion (ROM) and spinal canal dimension. RESULTS: The mean JOA scores of overall patient changed from 6.9 to 11.9, resulting in mean calculated recovery rates of 42.3%. The recovery rates of each group was 38.0% in the CSM group and 45.5% in the OPLL group, respectively (p=0.45). The mean cervical lordosis changed from 12.5 to 10.75 degrees in the CSM group and from 11.76 to 9.84 degrees in the OPLL group (p=0.79). The mean cervical ROM changed from 26 to 24.2 degrees in the CSM group and from 28.7 to 26.3 degrees in the OPLL group (p=0.78). The mean canal dimension changed from 201.1 to 285.0 mm2 in the CSM group and from 198.5 to 284.7 mm2 in the OPLL group (p=0.86). CONCLUSION: In the present study, all patients showed good long-term clinical outcomes by modified MSL. No significant clinical and radiographic difference of two disease entities in the same procedure was revealed.