We observed, during a 25-year period, 15 patients from 6 families with autoimmune myasthenia gravis (all Chinese Han from Guangdong Province) referred to our department. Their mean onset age was 13.4 years (range 2-25 years) with 10 patients with juvenile onset. The female:male ratio was 3:2. Acetylcholine receptors antibody titers were increased in 11 patients (range 1.62-19.8 nmol/L). Thymectomy was performed in six patients, who received corticosteroids /immune inhibitor plus pyridostigmine treatments after surgery. The other patients were placed on therapy with azathioprine, cyclophosphamide, corticosteroids and acetylcholinesterase inhibitors. All patients responded well to immunosuppressants, and psychiatric symptoms were observed only in one patient who received a high dose of corticosteroids. Patients with generalized type in the same family had different presentations with variable prognosis. HLA-A 0207 was found in 9 patients (9/15), HLA-B 4601 in 11 patients (11/15), and HLA-DRB1 0901 in 12 patients (12/15). When compared to familial autoimmune myasthenia gravis in other countries, we observed peculiar characteristics of Chinese populations, such as the within-family consistency was only found in families with ocular MG type (50% of all MG families), while the pathogenetic conditions and the prognoses of the generalized MG patients may differ greatly within the same family. These findings may shed new light on the genetic predisposition and the origin of immune abnormalities of MG patients.