The International Classification of Diseases (ICD) is applied worldwide for public health data collection among other use cases. However, the current version of the ICD (ICD-10), to which the reimbursement system is linked in many countries, does not represent chronic pain properly. This study aims to compare the ICD-10 with the ICD-11 in hospitalized patients in terms of specificity, clinical utility, and reimbursement for pain management. The medical records of hospitalized patients consulted for pain management at Siriraj Hospital, Thailand, were reviewed, and all pain-related diagnoses were coded into ICD-10 and ICD-11. The data of 397 patients showed unspecified pain was coded 78% in the ICD-10 and only 0.5% in the ICD-11 version. The difference gap in the proportion of unspecified pain between the 2 versions is wider than in the outpatient setting. The 3 most common codes for ICD-10 were other chronic pain, low back pain, and pain in limb. The 3 most common codes for ICD-11 were chronic cancer pain, chronic peripheral neuropathic pain, and chronic secondary musculoskeletal pain. As in many other countries, no pain-related ICD-10 codes were coded for routine reimbursement. The simulated reimbursement fee remained the same when adding 397 pain-related codings, even if the cost of pain management, such as cost of labor, existed. Compared with the ICD-10 version, the ICD-11 is more specific and makes pain diagnoses more visible. Thus, shifting from ICD-10 to ICD-11 has the potential to improve both the quality of care and the reimbursement for pain management.