Patients with diabetes have many different kinds of complications involving multiple organs, but those involving the musculoskeletal system are relatively uncommon. Diabetic muscle infarction (DMI) is a rare, painful, and potentially serious condition in patients with poorly controlled diabetes mellitus. A 35-year-old man diagnosed with type 2 diabetes eight years ago, visited with severe muscle pain in the right anteromedial thigh without any event of trauma. He had been treated with metformin, but his glycemic control was very poor with a glycated hemoglobin of 14.5%. Evaluation of his painful thigh lesion did not reveal any evidence of infection or vasculitis, but the magnetic resonance imaging and bone scan showed findings of DMI at vastus medialis muscle and an insufficiency fracture at the right medial tibial condyle. He was diagnosed with retinopathy, neuropathy and microalbuminuria but not macrovascular complications. We also diagnosed his diabetes as latent autoimmune diabetes in adults (LADA) based on his low C-peptide level, positive anti-glutamic acid decarboxylase (GAD) antibody and early onset diabetes. Instead of antibiotics, bed rest, analgesics and strict blood glucose control with multiple daily insulin injections led to symptom improvement. This is an unusual case of a young man with LADA experiencing severe musculoskeletal complication of DMI and insufficiency fracture. If a poorly controlled diabetic patient appears to have unaccounted soft tissue pain, musculoskeletal complications such as DMI associated with hyperglycemia should be considered.