During the last 10 years, the English Speaking Working Group (ESWG) of the International Society for Forensic Genetics (ISFG) has once a year arranged a Paternity Testing Workshop in which blood samples as well as a questionnaire concerning laboratory strategies were distributed to the participating laboratories. In 2000 and 2001, paper challenges were included in the workshops. Here, we present the results of the 2000 and 2001 Paternity Testing Workshops. The numbers of participating laboratories were 33 (2000) and 36 (2001). A total of 36% (2000) and 31% (2001) of the laboratories submitted typing results of variable number of tandem repeats (VNTRs) investigated with restriction fragment length polymorphism (RFLP) and single locus probes (SLPs). A total of 91% (2000) and 86% (2001) submitted typing results of polymerase chain reaction (PCR) based systems. Typing errors occurred in 0.3% of the submitted PCR-based results in 2000 and in 0.1% in 2001. The results of the paper challenges showed a high degree of variation in the formulas used for calculation of the weight of evidence of rare events such as inconsistencies or possible silent alleles. The majority of the laboratories used the same formulas for calculations of frequently occurring events.