Abstract: Objective To investigate the clinical manifestation of amyopathic dermatomyositis with other auto-immunological diseases and malignancy.Methods A case of amyopathic dermatomyositis with Hashimoto's thyroiditis and breast cancer has reported.Electromyography and pathological examination of skin and muscle had been pedorrned.The patient was followed up in ten months.Results A skin lesions manifested by typical edematous rash of dermatomyositis without muscle weakness had been found.The pathology of skin and muscle showed inflammation cells rounded skin and intramuscular capilaries without muscle degeneration.There were no changes in the muscular enzymes and the electromyography.It was found a Hashimoto's thyroiditis 2 months and a breast cancer 8 months after the onset.The skin lesions were attenuated by anti-thyroiditis and anti-cancer,respectively.Conclusion Amyopathic dermatomyositis may be associated with other anto-immunological diseases and cancer.