A grandparent study (sometimes referred to as grandpaternity) involves both parents of the alleged father. The test between the paternal grandchild and grandparents is often conclusive with almost the same assurance as the paternity test. This test is more extensive and not recommended unless a sample from the alleged father is unobtainable. The laboratories normally require an extra week to process this test. It is not as difficult as a sibling study.

Many grandparents order the grandparent home DNA test kit that allows them to verify that they are the grandparents without their sons’ knowledge.