An epidemiological study was conducted to ascertain the similarity of dietary habits among grown-up brothers and sisters who live separately in a small town. Twenty-three dietary habits of 53 pairs of brothers and 29 pairs of sisters were analyzed in comparison with the same number of control pairs who were matched with sex and age. Cramér's coefficients of contingency on many dietary habits in brother pairs were larger than those in control pairs. Multivariate analysis (quantification method of the third type) also showed that similarity of dietary habits both in brothers and sisters. Therefore, familial aggregation of any diseases is supposed to result in an interaction between hereditary factors and similarity of dietary habits among family members.