Little is known about the detraining and retraining effects of exercise in patients with diabetes. The purpose of the present study was to investigate the effects of training, detraining, and retraining, using a combined strength and aerobic exercise program on glycemic control in women with type 2 diabetes. Thirteen postmenopausal women with type 2 diabetes (n = 13, age: 55.8 ± 5.1 years) followed a supervised aerobic and strength training program for 9 months, which was interrupted for 3 months (detraining) and resumed again for a period of 9 months (retraining). Anthropometric characteristics, glycemic control, and physical fitness were determined at baseline and after 9, 12, and 21 months. Training induced a small reduction in body mass index (BMI: -3.3%, 95% CI -5.1 to -1.5%), a moderate decrease in fasting plasma glucose (FPG: -12.0%, 95% CI -20.70 to -3.2%), glycosylated hemoglobin (HbA1c: -4.7%, 95% CI -12.1 to 2.7%), and a large decrease in postprandial glucose (PPG: - 12.1%, 95% CI -20.2 to -4.1%). In addition, there was an increase in power output (20.2%, 95% CI 6.9 to 33.6%) and total muscle strength (33.8%, 95% CI 21.4 to 46.1%). Detraining reversed PPG, HbA1c, and physical fitness. Resumption of training, however, led to a moderate decrease in BMI (-5.4%, 95% CI -8.1 to -2.7%), PPG (-9.5%, 95% CI -19.4 to 0.3%), and HbA1c (-6.8%, 95% CI -14.1 to 0.5%), and to large changes in FPG (-20.9%, 95% CI -31.9 to -9.9%), power output (33.1%, 95% CI 17.9 to 48.4%) and total muscle strength (48.2%, 95% CI 34.0 to 62.4%) compared to baseline. Thus, systematic training improves body composition, glycemic control and physical fitness in patients with type 2 diabetes. The cessation of exercise brings about negative alterations, while retraining restores all beneficial adaptations and improves them even more. Therefore, diabetic patients should follow a regular and an uninterrupted exercise program throughout life in order to control glucose metabolism and improve health.