Sodium/glucose co-transporter 2 inhibitors (SGLT2i) represent a novel class of glucose-lowering agents that lower plasma glucose levels through pharmacological inhibition of glucose reuptake from the kidney, independent of insulin secretion and action. Clinical trials of SGLT2i demonstrated therapeutic benefits on glycemic control and bodyweight in individuals with type 2 diabetes, with few cases of serious adverse events (SAEs). However, a considerable number of SAEs were reported in patients receiving SGLT2i clinically in Japan during the first 3 months of their use. These included urogenital infections, hypoglycemia and dehydration. Unexpectedly, serious skin and subcutaneous disorders, mainly reported as generalized rash or skin eruption, were prominent in patients receiving SGLT2i, but with unknown mechanisms. There is also concern for potential SAEs associated with chronic SGLT2i administration, especially in the non-obese type 2 diabetes characterized by reduced insulin secretion often seen in East Asia. Chronic SAEs may include severe hypoglycemia due to depletion of hepatic glycogen storage, acceleration of diabetes-associated sarcopenia and ketosis/ketoacidosis. The current information on acute SAEs confirms the importance of caution in the appropriate use of SGLT2i. Furthermore, careful long-term observation of patients receiving SGLT2i is essential to avoid SAEs and for better clinical use of this drug class.