Since Jeffreys devised a DNA fingerprint in 1985, DNA analysis has been applied to paternity testing. The progress of the techniques, especially the development of polymerase chain reaction (PCR), makes it possible to type 10-15 short tandem repeat (STR) loci in paternity testing by a single test tube. When using a well qualified database, we can now obtain a paternity index (PI) as high as 105 in usual trio cases. Furthermore, the DNA testings are now applied to unusual cases, such as personal identification of Japanese war orphans left in China. Here, we reviewed how to calculate the PI likelihood ratio and exclusion probability in a trio case, a motherless case, parent identification without reliable evidence of mother and child relationship, and a sibling case. We also reviewed how to handle single exclusion cases usually derived from a single mutation that is no longer rare when many STR loci are used. Finally, we emphasized the importance of ethical, legal and social counseling for clients in paternity testing. From that point of view, paternity tests by mail should not be allowed because of lack of such counseling.