The study is based on effects of consanguinity in the parents of first cousin couples. One of wife’s or husband’s parents may be the product of first cousin marriage (Group-I and Group-II respectively) or both of their parents are the product of non-related subjects (Group-III) and Group-IV respectively). Significantly higher offspring mortality in Group-II marriages compared to Group-III & IV marriages were observed. Group-I marriages compared to Group-III & IV show non-significantly higher mortality in their offspring. The results show grandparental consanguinity plays a significant role on the mortality of grand children.