The medical records of service in disaster provided at a place other than a medical facility are defined as disaster medical records (DMRs). In this epidemiological study, to clarify medical need characteristics and trends after disaster, we analyzed the all anonymized DMRs of Minamisanriku Town that lost medical facilities in 2011 Great East Japan Earthquake and its consequent tsunami. After screening of duplicated or irrelevant documents, there were 10,464 DMRs with 18,532 diagnoses from March 11 through May 13. From 34 diagnostic groups according to International Classification of Diseases (ICD)-10, we integrated diagnostic groups into five modules that might require treatment concepts of different types: non-communicable disease (NCD), infectious disease, mental health issue, trauma, and maternal and child health (MCH). Age and sex distributions of the patients were similar to those of population before the disaster. The largest diagnostic module was NCD (68%), followed by infectious disease (21%), mental health issues (6%), trauma (4%), and MCH (0.2%). The age-specific rate of NCD exhibited a similar or suppressed level from that of nationwide survey, with higher rate of pollinosis among young population. Infectious disease increased in most age groups but there was no apparent outbreak because of early interventions. Sleep deprivation was twice as frequent in middle-aged women, compared with men. Trauma and MCH were less frequent, but each exhibited a unique time trend. Trauma onset was continuously recorded, while MCH visits were concentrated on a specific day. The medical need after disaster dynamically changes, and appropriate anticipatory countermeasures are necessary.