Type 1 diabetes mellitus(T1D) is an immune-mediated disease. The autoreactive T cells in T1D patients attack and destroy their own pancreatic cells. In order to systematically investigate the potential autoreactive T cell receptors(TCRs), we used a high-throughput immune repertoire sequencing technique to profile the spectrum of TCRs in individual T1D patients and controls.We sequenced the T cell repertoire of nine T1D patients, four type 2 diabetes(T2D) patients,and six nondiabetic controls. The diversity of the T cell repertoire in T1D patients was significantly decreased in comparison with T2 D patients(P = 7.0E 08 for CD4~+T cells, P = 1.4E 04 for CD8~+T cells) and nondiabetic controls(P = 2.7E 09 for CD4~+T cells, P = 7.6E 06 for CD8~+T cells). Moreover, T1D patients had significantly more highly-expanded T cell clones than T2D patients(P = 5.2E 06 for CD4+T cells, P = 1.9E 07 for CD8~+T cells) and nondiabetic controls(P = 1.7E 07 for CD4~+T cells, P = 3.3E 03 for CD8~+T cells). Furthermore, we identified a group of highly-expanded T cell receptor clones that are shared by more than two T1D patients. Although further validation in larger cohorts is needed, our data suggest that T cell receptor diversity measurements may become a valuable tool in investigating diabetes, such as using the diversity as an index to distinguish different types of diabetes. Type 1 diabetes mellitus (T1D) is an immune-mediated disease. The autoreactive T cells in T1D patients attack and destroy their own pancreatic cells. In order to systematically investigate the potential autoreactive T cell receptors (TCRs), we used a high-throughput immune repertoire sequencing technique to profile the spectrum of TCRs in individual T1D patients and controls. We sequenced the T cell repertoire of nine T1D patients, four type 2 diabetes (T2D) patients, and six nondiabetic controls. The diversity of the T cell repertoire in T1D patients were significantly decreased in comparison with T2D patients (P = 7.0E 08 for CD4 ~ + T cells, P = 1.4E 04 for CD8 ~ + T cells) and nondiabetic controls (P = 2.7E 09 for CD4 ~ + T cells, P = 7.6E 06 for CD8 + T cells). Moreover, T1D patients had significantly more more highly-expanded T cell clones than T2D patients (P = 5.2E 06 for CD4 + T cells, P = 1.9E 07 for CD8 ~ + T cells) and nondiabetic controls (P = 1.7E 07 for CD4 ~ + T cells, P = 3.3E 03 for CD8 ~ + T cells). F urthermore, we identified a group of highly-expanded T cell receptor clones that are shared by more than two T1D patients. Our further suggest in larger cohorts is needed, our data suggest that T cell receptor diversity measurements may become a valuable tool in investigating diabetes , such as using the diversity as an index to distinguish different types of diabetes.