Diabetes mellitus is a major health problem that had a consequence of high cost related to treatment and disease impact. This study aimed to estimate the cost of illness related T2DM from the perspective of patients. This study applied a prevalence-based cost of illness study from the perspective of patients. Data of direct medical costs, direct non-medical costs and indirect costs were collected by interviewing patients. The study involved patients covered by the national health insurance scheme as study respondents, which consisted of 96 patients visiting three public primary healthcare centres and 35 patients visiting a private secondary hospital in Yogyakarta Province, Indonesia. From the perspective of patients in Yogyakarta-Indonesia, the total cost of illness of T2DM within three months period was IDR 95,458 (USD 6.58) for patients at PHCs and IDR 340,159 (USD 23.46) for patients at the hospital, which were about 2% to 7% of the minimum wage rate. Indirect cost was the highest contribution of cost of illness (IDR 40,436/USD 2.79) to IDR 398,836/USD 17.63) and followed by direct medical cost (IDR 32,349/USD 2.23 to IDR 44,157/USD 3.05) and direct non-medical cost (IDR 22,673/USD 1.56 to IDR 40,334/USD 2.78). Cost of illness from out of pocket patients in this study was led by visits to other health facilities (the health facilities outside of study site) for obtaining health service related to T2DM disease. This study anticipated that T2DM had a consequence to out of the pocket cost of treatment and further productivity lost of patients and their caregivers.