Is there a risk of deformities if second cousins get married?

There's a negligible risk of birth defects for children born to second cousins who marry. While the risk of birth defects is theoretically doubled compared to unrelated parents (from 2-3% to 4-6%) this small increase is not enough to warrant significant concern. Some families have a higher incidence of a specific genetic disorder, so if there are known hereditary conditions in your family, it would be wise to consult with a genetic counselor before making a decision about marriage.