In ecology research, population density is an important metric for community analysis studies. Yet even though microbiomes are small ecosystems, microbiome studies rarely report the bacterial density. To evaluate the significance of bacterial density in gut microbiome research, a recent retrospective study examined rectal swabs from hospitalized patients. The authors found that bacterial density had important methodologic significance, as it predicted vulnerability to sequencing contamination. Specifically, low-bacterial-density specimens had higher levels of sequencing contamination. Clinical factors like age, exposure to antibiotics, and comorbidities also varied with bacterial density. Older patients and those with multiple co-morbidities had high bacterial density, while antibiotic exposure correlated with low density. Lastly, bacterial density showed potential as a prognostic indicator, as the density at time of admission correlated with subsequent infection. Although prospective studies are needed, these results highlight that bacterial density is related to key research metrics and suggest that this parameter should be reported in future gut microbiome research.