Microsatellite null alleles can affect parentage analysis by causing false exclusions. This study examines 233 articles reporting suspected null alleles and reviews how they were detected and handled. Computer simulations show that while null alleles at typical frequencies have minimal impact on average exclusion probabilities, they can cause significant errors in specific cases by leading to high false parentage exclusions. Null alleles are often due to poor primer annealing, differential amplification, or poor DNA quality. They can also be misinterpreted as evidence of heterozygote deficits or sex linkage. Methods for detecting null alleles include observing heterozygote deficits, analyzing parent-offspring relationships, and sequencing. Frequency estimation methods vary, but many studies fail to properly account for null alleles. The presence of null alleles can lead to underestimation of exclusion probabilities, reducing confidence in marker reliability. However, when null allele frequencies are high, exclusion probabilities can be overestimated. False exclusions can occur when an offspring is heterozygous for a null allele, even if the true parent is involved. Strategies to minimize false exclusions include using multiple loci and avoiding assumptions about homozygous alleles. Overall, while null alleles have limited impact on average exclusion probabilities, they can cause significant errors in specific cases, highlighting the need for careful analysis and consideration of potential null alleles in parentage studies.Microsatellite null alleles can affect parentage analysis by causing false exclusions. This study examines 233 articles reporting suspected null alleles and reviews how they were detected and handled. Computer simulations show that while null alleles at typical frequencies have minimal impact on average exclusion probabilities, they can cause significant errors in specific cases by leading to high false parentage exclusions. Null alleles are often due to poor primer annealing, differential amplification, or poor DNA quality. They can also be misinterpreted as evidence of heterozygote deficits or sex linkage. Methods for detecting null alleles include observing heterozygote deficits, analyzing parent-offspring relationships, and sequencing. Frequency estimation methods vary, but many studies fail to properly account for null alleles. The presence of null alleles can lead to underestimation of exclusion probabilities, reducing confidence in marker reliability. However, when null allele frequencies are high, exclusion probabilities can be overestimated. False exclusions can occur when an offspring is heterozygous for a null allele, even if the true parent is involved. Strategies to minimize false exclusions include using multiple loci and avoiding assumptions about homozygous alleles. Overall, while null alleles have limited impact on average exclusion probabilities, they can cause significant errors in specific cases, highlighting the need for careful analysis and consideration of potential null alleles in parentage studies.