Background. Women with previous gestational diabetes mellitus (GDM) have evidence of postpartum β-cell dysfunction, which increases their risk of developing type 2 diabetes (T2DM) later in life. Elevated levels of circulating cell-free preproinsulin (INS) DNA correlate with dying β-cells in both mice and humans. The aim of this study was to determine if cell-free circulating INS DNA levels are higher in women with previous GDM who develop T2DM. Methods. We used droplet digital (dd) PCR to measure the levels of cell-free circulating methylated and unmethylated INS DNA in plasma from 97 women with normal glucose tolerance (NGT), 12 weeks following an index GDM pregnancy. Women were assessed for up to 10 years for the development of T2DM. Results. In the follow-up period, 22% of women developed T2DM. Compared with NGT women, total cell-free INS DNA levels were significantly higher in women who developed T2DM (P=0.02). There was no difference in cell-free circulating unmethylated and methylated INS DNA levels between NGT women and women who developed T2DM (P=0.09 and P=0.07, respectively). Conclusions. In women with a previous index GDM pregnancy, postpartum levels of cell-free circulating INS DNA are significantly higher in those women who later developed T2DM.