A case was reported of a child born from paternal incest. Buccal cell samples were collected from the father, mother, daughter and the child of the daughter for deoxyribonucleic acid (DNA) extraction. Paternity testing by comparison of autosomal short tandem repeat (STR) profiles was performed in order to confirm this incest. In addition, 2 kinds of combined incest index (CII) values, including the trio of father, daughter and the child of the daughter, or the duo of daughter and the child of the daughter, were estimated. Both the CII values were high enough to indicate the incest relationship between the father and daughter. The Y-STR or X-STR profile comparison may be useful as additional evidence to confirm this paternal incest.