Type 1 diabetic patients who have endured their condition for prolonged periods are not uncommon, but there are few well-documented cases of type 2 diabetic patients with duration of over fifty years. In the present case study, we analyzed the history of a diabetic patient whose duration was 53 years. Her case was consequently diagnosed not as the common type 2 diabetes, but as the slowly progressive type 1 diabetes (SPIDDM) identified by Japanese medical researchers. The patient, now 73 years old, was first diagnosed with diabetes in 1953 when she was 17 years of age and started insulin injections. In 1962 she was referred to our hospital, and two years later she vaginally delivered a healthy baby (birth weight 3100 g) at the 40(th) week of gestation. She was the first case of a diabetic mother delivering an infant treated at Tokyo Women's Medical College Hospital. Her data shows that her C-peptide responses by meal tolerance test in 1978 was at least partly preserved though it decreased year by year. Her anti-GAD antibody was found to be positive in 2000 and remained so in 2009. This leads us to conclude that the etiology of her SPIDDM was most likely has insulin secretion exhaustion.