We describe a 16-year-old girl with an overlap syndrome consisting of systemic lupus erythematosus (SLE) from the age of 7 and polymyositis (PM) from the age of 10, later accompanied by systemic sclerosis (SSc) from the age of 15. She was diagnosed as having SLE with exudative malar erythema, photosensitivity, and discoid rashes with positive antinuclear antibody (ANA) and anti-DNA antibody titers. The diagnosis of PM was also made in accordance with findings of a high titer of muscle enzymes and a muscle biopsy specimen demonstrating marked degeneration of the muscle fibers and perivascular infiltration of mononuclear cells. She developed Raynaud's phenomenon and pitting ulcers on her fingers with positive anti-Scl 70 and anti-Ku antibodies, leading to a diagnosis of SSc. The patient was treated with prednisolone. To our knowledge this is the youngest case of SLE-PM overlap syndrome later accompanied by SSc.