ImportanceThe war in Tigray, Ethiopia, has disrupted the health care system of the region. However, its association with health care services disruption for chronic diseases has not been well documented.ObjectiveTo assess the association of the war with the utilization of health care services for patients with chronic diseases.Design, Setting, and ParticipantsOf 135 primary health care facilities, a registry-based cross-sectional study was conducted on 44 rural and semiurban facilities of Tigray. Data on health services utilization were extracted for patients with tuberculosis, HIV, diabetes, hypertension, and psychiatric disorders in the prewar period (September 1, to October 31, 2020) and during the first phase of the war period (November 4, 2020, to June 30, 2021).Main Outcomes and MeasuresRecords on the number of follow-up, laboratory tests, and patients undergoing treatment of the aforementioned chronic diseases were counted during the prewar and war periods.ResultsOf 4645 records of patients with chronic diseases undergoing treatment during the prewar period, 998 records (21%) indicated having treatment during the war period. Compared with the prewar period, 59 of 180 individuals (33%; 95% CI, 26%-40%) had tuberculosis, 522 of 2211 (24%; 95% CI, 22%-26%) had HIV, 228 of 1195 (19%; 95% CI, 17%-21%) had hypertension, 123 of 632 (20%; 95% CI, 16%-22%) had psychiatric disorders, and 66 of 427 (15%; 95% CI, 12%-18%) had type 2 diabetes records, which revealed continued treatment during the war period. Of 174 records of patients with type 1 diabetes in the prewar period, at 2 to 3 months into the war, the numbers dropped to 10 with 94% decline compared with prewar observations.Conclusions and RelevanceThis study found that the war in Tigray has resulted in critical health care service disruption and high loss to follow-up for patients with chronic disease, likely leading to increased morbidity and mortality. Local, national, and global policymakers must understand the extent and impact of the service disruption and urge their efforts toward restoration of those services.