Fifty cases of familial gastric cancer (consisting of our 10 cases in two families and 40 cases in five families reported in Japan) and 139 cases with no familiy history of gastric cancer seen in our department during five years (1975-1979) are reported. Clinical features of familial gastric cancer were compared with those of non-familial gastric cancer in terms of age of onset, sex and frequency of multiple primary malignant neoplasms. Average age of onset was 46.6 years old in familial gastric cancer, and 57.5 years in the controls. Incidences for those less than 40 years old were 35.4% and 5.7%, respectively. Early age of onset was characteristic of familial gastric cancer. As to sex, 56.1% of non-familial gastric cancer occurred in males, while 53.0% of familial gastric cancer occurred in females. Multiple primary malignant neoplasms occurred in 4.0% of familial gastric cancer and 5.0% of non-familial gastric cancer cases. Clinical evaluation of familial gastric cancer is useful to select the high-risk group for gastric cancer, detect early cancer, and apply curative therapeutic modalities.